Every ERP project makes two big choices: how to run the project and how to go live. Here is how to pick the right method for your business.
New to ERP implementation? Our ERP implementation guide covers what it is, its objectives, benefits, the types of ERP systems, and the full set of implementation phases. For the risks that derail projects, see ERP implementation challenges.
This page is about the methodologies themselves: the different ways to run an ERP project and the different ways to go live, so you can choose the approach that fits your business.
The first choice is how the project itself is run. Most ERP projects use one of three methodologies, or a blend of them.
| Methodology | Best for | Watch out for |
|---|---|---|
| Waterfall | Fixed scope, strict deadlines | Late changes are costly |
| Agile | Changing needs, quick feedback | Scope can grow without control |
| Hybrid | Most mid-sized ERP projects | Needs a disciplined project manager |
Waterfall
Waterfall runs the project in a strict sequence: plan, design, build, test, then go live. Each phase is finished before the next begins, which makes it easy to plan and budget when the scope is fixed and the deadline is firm. The trade-off is that changes late in the project are expensive, because the work behind them is already complete.
Agile
Agile delivers the ERP in short cycles with frequent reviews, so the system takes shape alongside changing needs and users give feedback early. It suits businesses that are still defining how they work, but it needs strong governance to stop scope from growing without control.
Hybrid
Hybrid combines the structure of waterfall for the overall plan with the flexibility of agile during build and testing. This is the most common choice for mid-sized ERP projects, but it only works with a disciplined project manager who keeps the plan, the scope, and the releases under control.
The second choice is the rollout: how much of the business switches to the new ERP system at one time.
| Rollout | Best for | Watch out for |
|---|---|---|
| Big bang (all at once) | Smaller companies, simple setups | Higher risk on go-live day |
| Phased (by module or site) | Multi-site or complex businesses | Longer overall timeline |
| Parallel (old and new side by side) | High-risk processes like finance | Double the data entry while both run |
Big bang (all at once)
A big bang go-live switches every user, module, and site to the new system on a single date. It is the fastest option and avoids running two systems at once, which suits smaller companies with simple setups. The risk is concentrated into one day, so it depends on thorough testing and training beforehand.
Phased (by module or site)
A phased rollout goes live in stages, either by module or by site, so each part of the business switches when its data, testing, and training are ready. It lowers the risk on any single go-live day and is the usual choice for multi-site or complex businesses. The trade-off is a longer overall timeline.
Parallel (old and new side by side)
A parallel rollout runs the old and new systems at the same time for a period, so results can be compared before the legacy system is retired. It is often used for high-risk processes like finance, where an error is costly. Running both systems means double the data entry while they overlap.
There is no single best methodology. Work through these questions and the right approach usually becomes clear.
How large is the company and the project?
Smaller companies with straightforward processes can move faster with an agile or big bang approach. Larger organizations with many users and complex processes usually need more structure, so a hybrid method and a phased go-live are safer.
How many sites, entities, or countries are involved?
A single site or legal entity is easier to switch at once. Multi-site and multi-country rollouts are safer with a phased approach, because each site can go live once its own data and training are ready.
How fixed is the scope?
If the requirements are stable and signed off, waterfall gives you a clear plan and a firm timeline. If the scope is still evolving, agile or hybrid keeps the project flexible without losing control of the budget.
How much risk can the business tolerate around go-live?
If a day or two of disruption is acceptable, a big bang go-live is quicker. If downtime would harm revenue or compliance, choose phased or parallel for the high-risk processes such as finance.
What is the deadline?
A tight, non-negotiable deadline favors waterfall with a tightly controlled scope. If the deadline is flexible, agile and phased rollouts give you room to adjust as you learn.
For Odoo projects, we follow a simple rule: standard first, customize only with a business reason. That keeps the implementation predictable, easier to upgrade, and faster to support. We plan in clear phases, test with real data, and phase the go-live whenever a business runs multiple sites or high-risk processes.
Explore the full set of ERP implementation guides:
What ERP implementation is, its objectives, the types of ERP systems, and the phases of a rollout.
A step-by-step view of how an ERP project moves from planning to go-live.
The most common problems that derail ERP projects and how to avoid them.
Agile or waterfall for ERP?
It depends on how fixed your scope is. Choose waterfall when the scope and requirements are stable and the deadline is firm, because it plans the whole project up front. Choose agile when requirements are still changing and you want feedback early and often. Many ERP projects, especially mid-sized ones, use a hybrid of both.
What is a phased rollout?
A phased rollout goes live in stages, by module or by site, instead of switching everything on at once. It lowers the risk on any single go-live day and lets the team apply lessons from the first phase to the next, but it takes longer overall because you run more than one launch.
Which ERP rollout is the lowest risk?
A phased rollout is usually the lowest risk because it limits how much changes at once and gives you time to fix issues between phases. A parallel rollout can also reduce risk for critical processes, but it costs more because teams run the old and new systems side by side.
Can we switch implementation methods midway?
Yes, but the earlier the better. Moving from waterfall to agile partway through, or switching rollout from big bang to phased, is possible when the project is re-planned and the change is controlled. Deciding this during planning avoids the cost and disruption of changing direction later.
What is a big bang go-live?
A big bang go-live switches every user, module, and site to the new ERP on a single date. It is faster and avoids running two systems at once, but the risk on go-live day is higher, so it suits smaller companies with simpler setups and well-tested processes.