Best Method Rule: How the OECD Chooses the Right Method
The best method rule defined: the method providing the most reliable measure of the arm's length result, given the comparability, the data and the assumptions available.
Definition
The best method rule is the OECD’s selection criterion for transfer pricing methods: the appropriate method is the one that provides the most reliable measure of an arm’s length result in the circumstances of the case — given the comparability of the parties, the data available, and the assumptions the method requires. There is no ranking of methods by prestige; a cost-plus on clean data beats a profit split on guesses.
Reliability has two components: how well the method isolates the tested party’s routine contribution (comparability), and how well it can actually be computed with real data (measurability). A method that fails either is not the best method, however sophisticated it is.
How the rule is applied
- Start from the transaction and the parties’ functional analysis.
- Ask, in order: is there a genuine uncontrolled price (CUP)? Is one party a pure residual that one-sided methods cannot capture (profit split)? Is there a genuinely routine, cleanly benchmarkable entity (TNMM, cost plus, gross margin)?
- Apply the data check to the surviving candidate: does the pool exist, is the PLI measurable, is the definition consistent?
- Document the decision — each alternative considered and set aside on stated facts.
The full decision framework, with the tree and the documentation pattern, is in how to choose a transfer pricing method.
Example
A routine service provider with a clean cost base and a pool of eleven standalone service companies: the best method is TNMM on a cost-based PLI — not because TNMM is “the standard method”, but because the comparability and the data both point there, and the file shows the CUP and profit-split alternatives were considered and set aside.
See also
FAQ
Can last year’s method be the best method this year? Only if re-derived this year from this year’s facts. The rule is about the current circumstances; “we used it before” is not a reliability argument, and the file should show the re-derivation.
Does the best method rule prefer one-sided methods? No — it prefers the most reliable method. In practice one-sided methods (CUP, TNMM, cost plus) usually win for routine transactions, because the data exists for them; two-sided methods (profit split) win where both parties are non-routine, because one-sided methods cannot capture the residual.
Run the screens as a study, not a spreadsheet
Quartyl applies the method, PLI and screening steps above as a pipeline — and keeps a documented reason for every exclusion.
Related docs
Transfer Pricing Methods: A Practical Guide
A practical comparison of CUP, RPM, Cost Plus, TNMM and Profit Split methods — and how to choose the right one for your Indian TP benchmarking study.
Read docTested Party: Definition, Selection Logic and Documentation
The tested party defined: the entity whose result is benchmarked against the comparable pool — selected as the least complex party, and documented as a decision.
Read doc