IFRS 16 Discount Rate (IBR): Complete Guide to Incremental Borrowing Rate Calculation

Implicit rate or IBR: which rate does IFRS 16 require?

IFRS 16.26 gives a strict order of preference: a lessee discounts the lease payments using the interest rate implicit in the lease, and only where that rate cannot be readily determined does it fall back to the lessee's incremental borrowing rate (IBR). The two are not interchangeable options; the IBR is a fallback, and the file should show the entity first tried to identify the implicit rate.

The interest rate implicit in the lease is defined in Appendix A as the rate that makes the present value of the lease payments and the unguaranteed residual value equal to the fair value of the underlying asset plus the lessor's initial direct costs (IFRS 16, Appendix A). The problem for the lessee is structural: two of those inputs — the unguaranteed residual value and the lessor's initial direct costs — sit inside the lessor's model and are almost never disclosed. That is why the implicit rate is "not readily determinable" for the vast majority of property and equipment leases, and why the IBR does most of the work in practice (IFRS 16.26).

The IBR is also defined in Appendix A as the rate a lessee would have to pay to borrow, over a similar term and with a similar security, the funds necessary to obtain an asset of a similar value to the right-of-use asset in a similar economic environment (IFRS 16, Appendix A). Four attributes are load-bearing here: similar term, similar security, similar amount and similar economic environment (which captures currency and jurisdiction). The IFRS Interpretations Committee confirmed in its September 2019 agenda decision that the IBR is not simply the entity's general cost of borrowing; it must reflect those lease-specific features, and it should approximate the rate implicit in a comparable secured borrowing.

Audit trail point: retain evidence that you attempted to determine the implicit rate before defaulting to the IBR (for example, correspondence asking the lessor, or a note explaining why the residual value was unknown). This is a routine ISA 500 request and costs nothing to prepare contemporaneously (IFRS 16.26).

How do you build an IBR in practice?

The most defensible method is a build-up approach: start with a term-matched risk-free rate, add an entity-specific credit spread, then adjust for the security and economic environment of the specific asset (IFRS 16, Appendix A). Each component is separately evidenced, which is exactly what an auditor tests under ISA 540. A single blended "group borrowing rate" fails because it ignores the similar-term and similar-security conditions in the definition.

The three components are as follows. The risk-free rate is a government bond (gilt, Bund, Treasury) yield whose maturity matches the lease term, read off the relevant yield curve at the commencement date. The credit spread reflects the lessee's own credit risk, derived from the entity's traded bonds, its bank margins over SONIA/SOFR, or a comparable-company or credit-rating spread matrix where the entity has no public debt. The security/asset adjustment reflects that a lease is effectively a secured borrowing against the underlying asset, which usually reduces the spread a lender would demand relative to unsecured debt (IFRS 16, Appendix A).

The worked build-up below is for a seven-year property lease taken out by a mid-cap manufacturer with a BB-equivalent credit profile, denominated in sterling. All inputs are dated to the commencement date and sourced to a printout retained on file.

Two disciplines make this survive review. First, build a small rate curve rather than a single number, so that a 3-year lease, a 7-year lease and a 10-year lease pick up different risk-free legs; using one rate across all tenors is a classic ISA 540 finding. Second, refresh the inputs for new leases at each commencement date, but do not re-derive the rate for existing leases — the commencement-date rate is locked in until a reassessment event occurs (IFRS 16.40-45).

Worked example: discounting a lease liability at the IBR

Take the 5.00% IBR built above and apply it to the lease. The manufacturer pays £700,000 annually in arrears for seven years, with no purchase option and no initial direct costs or incentives. The lease liability at commencement is the present value of those seven payments discounted at 5.00% (IFRS 16.26).

The initial recognition journal records the right-of-use asset and the lease liability at that present value (IFRS 16.22-26):

To see why the rate matters so much, hold the £700,000 payment and 7-year term constant and flex only the discount rate. A one-percentage-point move swings the opening liability — and therefore the right-of-use asset and future depreciation and interest — by roughly £150,000, about 3.7% of the balance (illustrative, derived from the annuity factors below).

When must the discount rate be reassessed?

The discount rate is fixed at commencement and only changes when IFRS 16.40-45 requires a remeasurement using a revised rate. It is essential to separate the events that trigger a new rate from those that keep the original rate, because auditors frequently find entities applying the wrong one.

A lessee remeasures the liability using a revised discount rate in the following cases: a change in the lease term, or a change in the assessment of whether a purchase option will be exercised (IFRS 16.40(a) and 16.41); and a change in future lease payments resulting from a change in a floating interest rate, using a rate that reflects the change in the interest rate (IFRS 16.42(b)). For a lease modification that is not accounted for as a separate lease, the lessee discounts the revised payments using a revised rate determined at the effective date of the modification (IFRS 16.45).

By contrast, the lessee keeps the original discount rate where the change is only in the amount of payments driven by an index or a rate (for example a CPI uplift or a market-rent review) — here IFRS 16.43 requires the unchanged original rate. General movements in market interest rates after commencement never, on their own, change the rate applied to an existing liability.

The example below shows a term extension. At the start of year 4, the manufacturer extends the seven-year lease by three years (now becoming reasonably certain to stay), and its refreshed IBR at that date is 6.00% given a higher gilt curve. The carrying amount of the liability just before remeasurement is £2,551,320 (the amortised balance after three payments at 5%). The revised liability is the present value of the remaining seven annual payments of £700,000 discounted at the revised 6.00% rate (IFRS 16.40-41).

The remeasurement is recognised as an adjustment to the right-of-use asset, not in profit or loss (IFRS 16.39-40):

Had this instead been a pure CPI uplift to the payments with no term change, the entity would have discounted the revised payments at the original 5.00% rate, and the adjustment would have been far smaller (IFRS 16.43). Choosing the correct rule is the whole point of the reassessment analysis.

Can one IBR cover a portfolio of leases?

Yes. IFRS 16.B1 lets a lessee apply the standard to a portfolio of leases with similar characteristics, provided it reasonably expects the effect on the financial statements will not differ materially from applying the standard to each lease individually. For discount rates this is a practical lifeline: a retailer with 400 near-identical store leases does not need 400 separate build-ups.

The condition is homogeneity, not convenience. A defensible portfolio groups leases that share the attributes the IBR definition cares about — currency, remaining term band, asset class and security profile — and applies one build-up rate to each group (IFRS 16.B1, read with Appendix A). A five-year GBP store lease and a fifteen-year EUR distribution-centre lease cannot sit in the same bucket, because their risk-free legs, credit spreads and security profiles all differ. Grouping should be documented with the materiality assessment that supports it, because IFRS 16.B1 is conditioned on that "not materially different" expectation.

Practical tip: a term-banded rate matrix (for example 1-3, 4-6, 7-10 and 10+ years, split by currency) usually satisfies both IFRS 16.B1 and the similar-term requirement in one document, and gives the auditor a single schedule to test (IFRS 16.B1).

What do auditors challenge on the discount rate?

The discount rate is an accounting estimate, so ISA 540 (Auditing Accounting Estimates and Related Disclosures) governs the audit approach: the auditor tests the method, the assumptions and the data, and probes for management bias. The three findings below are the ones that recur, each mapped to the standard that drives the challenge.

Red flag 1: rate below observed cost of debt (ISA 540)

The most common challenge is an IBR that sits below the entity's own observable borrowing cost. If the group pays SONIA + 2.5% on its revolving facility but discounts leases at 3.5%, ISA 540 requires the auditor to understand why. There can be a valid answer — the facility carries commitment and fronting fees, or the lease is better secured than the unsecured RCF — but it must be documented and quantified, not asserted. An unexplained gap between the IBR and the observed cost of debt is treated as a potential indicator of management bias under ISA 540.

Red flag 2: undocumented inputs (ISA 500)

ISA 500 (Audit Evidence) requires sufficient appropriate evidence for each input. A build-up that states "risk-free 4.0% + spread 1.5%" with no source, no date and no printout of the yield curve fails the relevance-and-reliability test in ISA 500. The fix is contemporaneous: retain the dated gilt-curve extract, the bond or margin evidence for the spread, and a short memo explaining the security adjustment. Reconstructing this a year later, at audit, is exactly the weak, internally generated evidence ISA 500 warns against.

Red flag 3: unchecked specialist spread (ISA 620)

Larger groups often engage a treasury or valuation specialist to derive credit spreads or a full rate matrix. Where management uses such an expert, ISA 500 (para 8) requires the auditor to evaluate that expert's work, and where the auditor engages its own specialist, ISA 620 (Using the Work of an Auditor's Expert) applies. Either way, the specialist's competence, capabilities and objectivity, and the appropriateness of their assumptions, must be assessed — a spread cannot be accepted simply because "the model produced it." Black-box outputs with no scope, no assumptions and no reconciliation to observable market data are a standing ISA 620 finding.

Usman Qureshi (ACCA)

The most common challenge on an incremental borrowing rate is not the maths — it is a rate that does not tie back to the entity's own cost of debt, with no dated evidence behind the inputs. This guide reflects what auditors actually ask for under ISA 540, ISA 500 and ISA 620.

Case study: Tesco's disclosed lease discount rate

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