ERP Implementation in E-Commerce: Process, Timeline, Cost (2026)

A new ERP in online retail is open-heart surgery. You rebuild orders, stock, purchasing and accounting. Your store and your marketplaces keep running the whole time. If an order goes wrong on go-live weekend, the customer notices right away. If a stock level is wrong, you sell goods on Amazon that you don’t have.

Most guides on ERP implementation come from ERP vendors. They usually write about manufacturers. This guide is vendor-neutral. It is written for online stores and D2C brands with €500,000 to €50 million in revenue, with a focus on the DACH region. You will learn how an ERP implementation in e-commerce works, how long it takes, what it costs and where projects fail.

The short answer

Timeline: A store with one or two channels and one warehouse needs about three to five months. With many marketplaces, an external warehouse or B2B, it takes six to twelve months. That counts from selection until things run smoothly.

Cost: In year one, an ERP project costs between about €15,000 and well over €300,000. The software is usually the smaller part. Setup, integrations, data migration and your team’s time cost more.

Mistakes: ERP projects in e-commerce rarely fail because of the software. More often there is no clear rule for which system owns which data. On top of that come too many special requests and integrations that were not tested enough. And the go-live often sits too close to the holiday season.

When does an online store need an ERP?

Many stores start with the store backend, a shipping tool and Excel. That works until one of these things happens:

Several channels: You also sell on Amazon, Otto, Kaufland or Zalando. Stock levels must be right everywhere.
Several warehouses: You have your own warehouse plus a fulfillment partner, stores or drop shipping.
Many orders: From about 30 to 50 orders a day, manual work becomes the bottleneck.
B2B: You need customer prices, payment on invoice and payment terms.
Purchasing: You want order suggestions and minimum stock levels.
Accounting: Payments from many sources and the export to your accountant take too much time.

Inventory management software and ERP are often used as the same thing. Inventory software covers products, stock, orders and shipping. An ERP adds purchasing, finance and controlling. Which systems fit Shopify is covered in the Shopify ERP guide. For a short definition, see ERP in the glossary.

Process: ERP implementation in 7 phases

Every vendor has its own phase model. The names differ, the content is almost the same. For online retailers, one thing matters most: store, marketplaces, warehouse and payments need their own tasks in every phase. Otherwise problems only show up during testing.

Phase	Duration	Result	E-commerce tasks
1. Goals and processes	3 to 6 weeks	Target processes, volumes, budget	Map flows per channel, returns, payment and shipping methods
2. Selection	4 to 10 weeks	System and partner chosen	Check store and marketplace connectors, talk to customers on the same store platform
3. Fit to standard	3 to 6 weeks	Concept with gaps and solutions	Decide which system owns which data; stock sync timing and buffers
4. Setup and integrations	6 to 16 weeks	Configured system	Connect store, marketplaces, warehouse, shipping, payments and accounting
5. Data migration	parallel to phase 4	Clean data, 2 to 3 trial runs	Products, variants, EANs, customers, open orders, stock
6. Testing and training	3 to 6 weeks	Sign-off by each team	Test order per channel and payment method, return, cancellation, partial delivery
7. Go-live and aftercare	1 weekend plus 4 to 8 weeks	Stable operations	Plan the cutover, transfer final data, check stock, fix issues fast

Phase 1: Goals and processes

Don’t talk about systems yet. First decide what your business should look like in two to three years. How many channels? Which countries? How much B2B? Your own warehouse or a provider?

Write down the volumes too. How many orders come in per day, and on peak days? How many products and variants do you have? How many people will work in the system?

The result is not a thick requirements document. The result is a short list. It shows the processes that must run safely. And it shows the few points that truly make your business special.

Phase 2: Selection

Compare two to four systems. Use your own processes for this, not feature lists. Ask to see your three most important processes with your own data. For example, an Amazon order with a partial delivery and a return.

The partner who sets up the system matters as much as the system. Ask for customers with your store platform and your size. Call those customers yourself.

According to Softwarepath, selection takes 17 weeks on average. Small companies with fewer than 50 employees need about 14 weeks. If you do phase 1 well, you will be much faster.

Phase 3: Fit to standard

This is where your budget holds or breaks. Check every process: is the system’s standard good enough? Every deviation needs a good reason. A good reason has to do with revenue or cost. “We have always done it this way” is not a good reason.

For online retailers, one question belongs here above all: which system owns which data? More on that in the next section.

Phase 4: Setup and integrations

The partner sets up products, warehouses, shipping methods, payment methods, taxes and number ranges. At the same time, the integrations are built. They connect the ERP to the store, marketplaces, warehouse, shipping, payment providers and accounting.

This phase causes the most delays. Integrations only show their special cases with real data.

Phase 5: Data migration

Data migration runs alongside the setup. Plan at least two trial runs. Only then does the real migration follow. More on this in the section on switching ERP.

Phase 6: Testing and training

Test full processes, not single features. A test starts with the order and ends with the booking in accounting. Every combination of channel, payment method and shipping method needs at least one test order. Also test cancellation, partial delivery, return and credit note.

Train a few key people from each team early. They are often called key users. They then train their teams. That usually works better than training by the partner.

Phase 7: Go-live and aftercare

The switch itself usually takes a weekend. After that come four to eight weeks of aftercare. During this time, the partner and your team fix issues quickly. This is often called hypercare. How to plan the weekend is covered below.

Connecting your store, marketplaces and warehouse

Trovarit AG regularly surveys ERP users in Germany, Austria and Switzerland. In its study “ERP in der Praxis 2026/27”, integrations get the worst rating of all criteria. About 19 percent name integrations as a problem in daily operations. That puts them in second place. In e-commerce, integrations are the core of the project.

Which system owns which data?

For each type of data, exactly one system is in charge. This is often called the system of record. All other systems only read along or write back through fixed paths.

Data	System of record	Direction	Typical timing
Products, prices, variants	ERP or PIM	ERP/PIM to store and marketplaces	on change or hourly
Copy and images	PIM or store	PIM to store and marketplaces	on change
Stock levels	ERP or warehouse system	ERP to all channels	every 1 to 15 minutes
Orders	Store or marketplace	Channel to ERP	almost instantly
Shipping and tracking	ERP or 3PL	ERP to channel	on shipment
Customers	Store (B2C), ERP (B2B)	depends on the business	on change
Payments	Payment provider	Provider to ERP or accounting	daily
Invoices and credit notes	ERP	ERP to channel and accounting	on creation

Do you use a PIM? Then copy and images belong there, not in the ERP. More on this in PIM for Shopify.

Connecting Shopify or Shopware to your ERP: three ways

Option	Fits for	Typical effort	Risk
Ready-made connector from the ERP vendor	Standard processes, one store, common marketplaces	a few days to 6 weeks, often included in the price	special cases don't work; depends on vendor updates
Middleware (e.g. Alumio, Synesty)	several systems, custom rules, swapping systems later	from about €500 per month plus setup	one more system someone has to look after
Custom integration via API	very specific processes, high volumes	from about 10 to 20 days of work per integration	maintenance stays with you or your agency

Up to about €10 million in revenue, a ready-made connector is usually enough. It must cover your most important processes, though. Middleware pays off when three or more systems work together. Or when you want to swap single systems easily later.

Preventing overselling

Shopify, Shopware and marketplaces only allow a certain number of requests per minute. If stock levels only arrive every 15 or 60 minutes, you sell goods at peak times that are already gone. Two things help:

A buffer per channel: On marketplaces, for example, always show two units fewer than you have.
Send on every change: Stock updates go out right away, not only on a fixed schedule.

How long does an ERP implementation take?

Many guides quote numbers without saying who they apply to. Here are the key studies:

Source	Result	Who it applies to
Panorama Consulting, ERP Report 2026	Median 9 months	mostly large companies: median revenue of respondents $200.5M, mostly international
Panorama Consulting, ERP Report 2024	15.5 months	as above, older survey
Trovarit, ERP in der Praxis 2023	small companies just over 6 months, mid-sized 10 to 13 months, large about 14 months	DACH region, vendor-neutral, all industries
Softwarepath ERP Report	Selection 17 weeks, under 50 employees about 14 weeks	mainly USA and UK

You often read “21 months on average”. That number comes from older Panorama surveys. Projects are shorter today. Panorama explains this with the high share of cloud software.

For online retailers, practice shows:

Starting point	Typical duration	Biggest time sinks
One store, one or two marketplaces, own warehouse, under €3M revenue	3 to 5 months	cleaning product data, connecting shipping
Several marketplaces, external warehouse, €3M to €15M revenue	5 to 9 months	3PL integration, stock levels, matching payments
B2C and B2B, several warehouses or countries, €15M to €50M revenue	9 to 15 months	special requests, approvals, data from the old system

The software hardly decides the timeline. Three other things matter more:

how fast you make decisions
how clean your data is
how much time your key users have next to daily business

What does an ERP implementation cost?

The cost blocks

Software: licence or subscription, usually per user, per order or by revenue
Setup: concept, configuration and project management by the partner
Integrations: connector, middleware or custom development
Data migration: cleaning, mapping and testing data
Training: key users and teams
Your team’s time: project lead, key users, management
Operations: maintenance, updates, support, changes after go-live
Buffer: at least 15 to 20 percent

According to the Panorama ERP Report 2026, about 30 percent of projects went over budget. These were the most common reasons:

extra technology was needed (54.9 percent)
the scope grew (51.0 percent)
technical problems (43.1 percent)
too few staff were planned (35.3 percent)

What does the software cost?

System	Pricing model	Entry price according to vendor
JTL-Wawi	Base free, order packages for Shopify, Shopware and marketplaces	order packages from €25 per month (100 orders), Advanced from €99, Pro from €329 per month
Xentral	packages by number of orders	Starter €349, Business €649, Pro €849 per month
weclapp	per user	ERP Retail from €163 per user per month
Odoo	per user	Standard from €24.90, Custom from €44.90 per user per month (regular prices)
Microsoft Dynamics 365 Business Central	per user	Essentials €69.30, Premium €95.30 per user per month
Billbee	by number of orders	from €9 per month (order processing, not a full ERP)
Plentymarkets / PlentyONE	tiered by revenue	no public price list

The licence is rarely the biggest item. A rule of thumb: setup and integrations cost one to three times the licence in year one. There is no neutral study on this. My experience confirms the rule, though.

Cost by company size: three examples

Cost block	A: under €3M, Shopify with JTL or Xentral, 1 warehouse	B: €3M to €15M, several marketplaces, external warehouse	C: €15M to €50M, B2C and B2B, Business Central or Odoo with middleware
Software (year 1)	€2,000 to €10,000	€10,000 to €40,000	€30,000 to €120,000
Setup by partner	€5,000 to €25,000	€30,000 to €100,000	€100,000 to €350,000
Integrations and middleware	usually included in the connector	€10,000 to €40,000	€30,000 to €100,000
Data migration and training	€2,000 to €8,000	€8,000 to €30,000	€25,000 to €80,000
Total external cost year 1	about €10,000 to €45,000	about €60,000 to €210,000	about €185,000 to €650,000
Your team's time	40 to 80 person-days	120 to 250 person-days	300 to 600 person-days
Typical duration	3 to 5 months	5 to 9 months	9 to 15 months

Do the numbers add up? The Trovarit study quotes about €6,000 per workstation for an implementation. With 15 users, that is about €90,000. With 50 users, it is about €300,000. That fits examples B and C.

Almost always underestimated: your team’s time. According to Trovarit, a mid-sized project has a core team of about five internal and 2.5 external people. Your key users often need 30 to 50 percent of their time for the project. That time is missing from daily business. Plan for cover or temporary help.

Cost calculator: your ERP implementation in numbers

Estimate cost, effort and timeline for your store. The calculator uses the same guide values as the examples above. It also shows when a go-live is realistic if you start now.

The best time to go live

In online retail, the go-live date is a big decision. The best-known bad example is Hershey. In 1999, the confectionery maker switched everything at once just before Halloween. Orders worth more than $100 million could not be shipped.

For most online retailers:

No go-live from mid-October to the end of January. Black Friday, the holidays and the wave of returns leave no room for errors.
Good windows are February to April and June to August. It depends on your season.
A stock count or a new financial year are good cut-off dates. Stock gets counted anyway.
At least eight weeks before peak season. Then aftercare is over in time.

Plan backwards. Should go-live happen by the end of August at the latest? Then selection usually has to be done in spring.

The go-live weekend

Microsoft requires a fixed plan before every go-live in its ERP projects. It includes clear go/no-go criteria, trial runs and a runbook. The runbook says who does what and when. That applies to every ERP project in e-commerce. The switch itself is called the cutover.

This is how a typical weekend runs:

Freeze master data: A few days before, nobody changes products or prices in the old system.
Handle incoming orders: The store stays online. Orders are collected briefly and transferred afterwards. Or you pause your marketplaces for a few hours.
Transfer final data: Open orders, stock and new customers since the last trial run.
Check stock: Do the numbers in the new system match the warehouse?
Real test orders: One order per channel, payment method and shipping method, through to the shipping label and the booking.
Go or no-go: Decide based on the criteria you set in advance.
Plan B: What do you do if key processes don’t work? How long can the old system keep running?
Aftercare: For four to eight weeks there are short daily check-ins. Someone watches the integrations. The partner responds fast.

Switching ERP and migrating data

Many retailers are not implementing their first ERP. They are switching. For example, from JTL to Xentral, from a homegrown tool to the cloud or to Business Central. According to Trovarit, ERP systems in the DACH region are over 13 years old on average. A switch is a chance to leave old baggage behind.

What goes into the new system and what doesn’t

Migrate: active products with variants, EANs and prices, active customers, suppliers, open orders, open items, current stock
Don’t migrate: old products, duplicates, test data, customers who haven’t bought in many years
Archive: Old orders and documents stay readable in the old system or in an archive.

Obligations when you switch (Germany)

Retention: Since 2025, accounting documents must be kept for eight years in Germany. Ledgers, inventories and annual accounts still need ten years.
GoBD: The German tax office must be able to analyse old data for the full retention period. Don’t just switch the old system off. Update your process documentation too.
Data protection (GDPR): Only migrate customer data you still need. Sign a data processing agreement with the ERP vendor and every service provider. Don’t use real customer data in the test system, only anonymised data.

The 10 most common mistakes in e-commerce ERP implementations

According to Trovarit, only 17 percent of ERP projects ran largely smoothly in 2020/21. Gartner expects more than 70 percent of recent ERP projects to fall short of their goals by 2027. In online retail, I see these mistakes most often:

Go-live in peak season. If you switch in October, you test during the holiday rush.
No clear data owner. Prices are maintained in the store and in the ERP. Nobody knows which price is right.
Copying old processes exactly. A well-known example is Lidl. Its SAP project eLWIS was stopped in 2018 after about seven years. Lidl values stock at purchase prices, SAP at retail prices. The changes needed became too big.
Integrations only tested with simple cases. Bundles, gift cards, partial returns and orders with two payment methods only show up in live operations.
Stock sent too rarely. The result: overselling on marketplaces and worse seller ratings.
Payments not matched. PayPal, Klarna, Shopify Payments and marketplaces pay out separately. The ERP has to match each payment to the right order. Otherwise the pile in accounting keeps growing.
Old data migrated without checks. Duplicate and wrong product data ends up in the new system. Through the integrations, it goes back into the store.
Store apps and ERP do the same job. Apps for invoices, shipping or stock keep running. They create duplicate documents.
Key users have no time. The project runs “on the side” and decisions get stuck. Under Armour had delivery problems after its SAP switch in 2017. The company named problems with change management as a reason.
No plan B and no go-live criteria. The date is kept even though important tests are missing.

The project team: who do you need?

Management as sponsor: decides in conflicts and keeps priorities stable.
Internal project lead: knows the processes, can make decisions and has at least half their time for the project.
Key users from every team: customer service, warehouse, purchasing, accounting and e-commerce. They test, make decisions in their area and train their teams.
ERP partner: setup, integrations, data migration.
Store agency: if the store needs changes.
Tax advisor: for the chart of accounts, accounting export and e-invoicing.

Many retailers also bring in neutral support. It earns nothing from selling the system or from project days. It makes sure e-commerce requirements end up in the concept. It reviews the partner’s offers and results. And it helps with decisions. How I do this is described on the implementation support page.

E-invoicing and funding in Germany: what matters in 2026

E-invoicing as a trigger

Since 1 January 2025, all businesses in Germany must be able to receive e-invoices. From 1 January 2027, businesses with more than €800,000 in prior-year revenue must also issue them. From 2028, this applies to everyone.

The obligation only covers invoices to businesses in Germany. Pure D2C stores are hardly affected when it comes to issuing invoices. They must still be able to receive invoices from suppliers. Retailers with a B2B share should plan their ERP project now. During selection, check whether the system can create and read XRechnung and ZUGFeRD.

Funding

go-digital ended on 31 December 2024, Digital Jetzt already at the end of 2023. Many guides still mention both.
KfW ERP-Förderkredit Digitalisierung: Since July 2025, software and consulting can also be financed through your bank. Some tiers include a grant.
State programmes: for example the Digitalbonus Bayern until the end of 2027 with up to 50 percent funding. The rules change often. Check with the provider before you start.

Checklist: is your ERP project ready?

FAQ

How long does an ERP implementation take for an online store?

A store with one or two marketplaces and its own warehouse needs about three to five months. With many marketplaces and an external warehouse, it takes five to nine months. With B2B and several warehouses, it takes nine to fifteen months. That counts from selection to the end of aftercare.

How much does an ERP implementation cost for an online store?

Smaller stores pay about €10,000 to €45,000 in external costs in year one. Retailers with many marketplaces and an external warehouse pay about €60,000 to €210,000. Larger retailers with B2B pay well above that. On top comes your team’s time. It is often underestimated.

What are the phases of an ERP implementation?

There are seven phases: goals and processes, selection, fit to standard, setup and integrations, data migration, testing and training, and go-live with aftercare.

Why do ERP projects fail?

Mostly for organisational reasons. Decisions are missing, key users have too little time, there are too many special requests and the schedule is too tight. In e-commerce, three more points come up: no clear rule for which system owns which data, integrations that were not tested enough and a go-live in peak season.

When is the best time to go live?

Outside peak season and at least eight weeks before it. For most online retailers, February to April or June to August work well. Avoid switching between mid-October and the end of January.

Big bang or step by step?

In e-commerce, orders, stock, shipping and invoicing usually switch together. They are closely linked. More channels, countries or modules then follow step by step. According to Panorama 2026, more than a quarter of companies choose this mix.

Should you migrate old data to the new ERP?

Only active master data, open transactions and current stock. Old orders and documents are better kept in an archive or in the old system. Access must be secured for the full legal retention period.

Do I need an ERP consultant?

Not for every project. With many channels, an external warehouse or B2B, neutral support pays off. It should not earn money from selling the system. It helps most during selection, the concept and before go-live.

Conclusion: an ERP project is an e-commerce project

An ERP implementation in online retail is not just an IT project. You rebuild your order processing while your store keeps running. Five things decide success: a clear goal, few deviations from the standard, clear rules for data, well-tested integrations and a go-live well away from peak season.

The software is the smaller part of the cost. Plan your budget and, above all, your team’s time honestly. Then you can complete an ERP project in three to twelve months.

ERP Implementation in E-Commerce: Process, Timeline, Cost and Common Mistakes