Many tax teams know they need ONESOURCE Tax Provision but are uncertain what the implementation journey looks like — particularly how long it takes, what it demands of their team, and where the hard parts typically sit.
This article sets out what a typical OTP implementation involves, based on our experience delivering implementations across UK and European multinational groups.
The five phases of an OTP implementation
A well-structured implementation typically runs through five phases, though the balance and timeline vary by organisation.
1. Scoping and design
This is where the real work of an implementation is done, even if it does not always feel like it. Scoping involves understanding your entity structure, jurisdictions, ERP, current provision process, and the specific configuration requirements that will flow from all of that.
The output is a functional design document — an agreed specification of what the system will do, how data will flow into it, and what the provision calculation will look like. Every decision made here shapes what follows. Scoping typically takes two to four weeks, and the quality of this phase determines a great deal of what happens later.
2. Data and integration setup
This is usually the most technically intensive phase. Your chart of accounts needs to be mapped to OTP’s data model, currencies need handling, opening balances need loading, and the extraction and transformation layer — whether Alteryx-based, API-driven, or file-based — needs to be built and tested.
Data quality problems that were not visible during scoping often surface here. Missing account mappings, inconsistent inter-company coding, and currency rounding issues are common examples. Experienced consultants recognise these quickly; inexperienced ones spend weeks diagnosing them.
3. Configuration
This is the platform-facing work: building current and deferred tax computations, rate tables, jurisdictional rules, return-to-provision logic, and the internal workflows within OTP itself.
Configuration is highly technical but also highly tax-logical — the system needs to reflect how your provision actually works, which requires both platform expertise and a solid understanding of the underlying tax. Configuration and integration usually run in parallel once the design phase is complete.
4. Testing
Running the system in parallel with your existing process across one or more reporting periods. This is where discrepancies surface, configurations are refined, and your team begins to build confidence in the outputs.
Testing is not a single event — it is iterative. Plan for multiple rounds of testing, particularly if your ERP data has quality issues or if your provision methodology is complex.
5. Go-live and hyper-care
Migrating to live production data and supporting the first live close. The first close is always the most demanding, and having consultants available during that period — not just on call, but actively engaged — is important. A well-managed hyper-care period sets the foundation for confident internal ownership of the system.
What does it demand of your team?
OTP implementations require meaningful input from your tax function. Plan for a senior tax manager to be involved at perhaps 20–30% of their time during the implementation period — more during scoping and testing, less during the build phase.
You will also need access to ERP data and cooperation from IT or finance systems teams, particularly for the integration phase. Getting that cooperation lined up early is one of the most commonly underestimated aspects of project planning.
How long does it take?
A typical implementation for a mid-sized UK multinational runs three to five months from kick-off to first live close. Larger organisations with multiple jurisdictions, fragmented ERP landscapes, or complex group structures may take longer.
The most common causes of delay are: late access to clean ERP extracts, stakeholder sign-off bottlenecks, and scope changes once the design phase is complete. Managing these risks well — through clear governance and honest initial scoping — is where experienced consultants add disproportionate value.
After go-live
OTP is not a set-and-forget system. Tax rate changes, new jurisdictions, changes to your provision methodology, and software updates all require ongoing attention. Most organisations benefit from a defined hyper-care period (typically covering one to three reporting cycles) before transitioning to internal ownership.
If you are considering an OTP implementation and would like to understand what it would involve for your specific organisation, get in touch — we are happy to have a straightforward conversation about your situation, without obligation.