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

What is the Incremental Borrowing Rate (IBR)?

IFRS 16.26 defines it as: "the rate of interest that 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."

In plain English: the interest rate you would pay if you borrowed money to buy the leased asset, all else being equal.

Because lessees almost never know the implicit rate, the IBR becomes the discount rate used to calculate lease liabilities. This makes it critical to get right.

Why the Discount Rate Matters

Remember the lease liability formula: Present Value of Lease Payments = Payment ÷ (1 + r)^t

A small change in r (the discount rate) compounds across years. For a £500k annual lease over 10 years:

A 2% variance in IBR swings the balance sheet by nearly £400k. Auditors are acutely aware of this.

Four Methods to Calculate or Estimate IBR

Method 1: Ask Your Bank Directly

The simplest approach. Call your relationship manager and ask:

"What rate would you charge us to borrow £X over Y years with Z collateral?"

Pros: Definitive, lender-backed, hard to argue with

Cons: Requires relationship, may take time, bank may refuse for new facilities

Example: Your bank's standard term rate for a 5-year asset loan is 6.2%. You use 6.2% for all 5-year leases. Clean and defensible.

Method 2: Observe Your Existing Debt

Look at rates you're already paying.

Steps:

• Identify all borrowing in your debt schedule (term loans, bank facilities, bonds, overdrafts)
• Extract the all-in rate (including fees, margin over SONIA/SOFR, etc.)
• Adjust to match lease term (e.g., if your £5m facility is 3 years at 6%, but you want a 7-year IBR, adjust upward by ~0.25— 0.50% for the longer term)

Pros: Based on real cost of capital, easy to defend ("Our bank charged us 6% on our term loan")

Cons: Existing rates may not match lease term or collateral type; requires judgment to adjust

Method 3: Risk-Free Rate + Credit Spread Approach

This is the most rigorous approach and what auditors often expect for larger lease portfolios.

Formula: IBR = Risk-Free Rate + Credit Spread

Risk-Free Rate: Use the gilt yield (UK) or treasury yield matching your lease term

Credit Spread: The additional margin your company pays above the risk-free rate, derived from:

• Bond yields (if you're a public company)
• CDS (credit default swap) spreads
• Comparable company analysis (find peers with similar credit rating)

Worked Example:
— 5-year lease
— UK 5-year gilt yield: 2.5%
— Your company is BB-rated (sub-investment grade)
— Observable BB-rated bond spread: +2.8%
— IBR = 2.5% + 2.8% = 5.3%

Method 4: Build-Up Approach

Break down borrowing costs into components:

IBR = Risk-Free Rate + Company Credit Spread + Collateral Risk Premium

For example:

• Risk-free rate: 2.5%
• Credit spread (company-specific): 2.0%
• Collateral risk premium (additional security required for this asset): 0.5%
• Total IBR: 5.0%

Worked Example: Three Scenarios

Scenario 1: Public Company with Bond Issuance

Company: Large retailer, investment-grade rated (A−’)
Bond information: Issued £200m, 5-year senior bonds at 3.2%

Approach: Use 3.2% as the IBR for all 5-year leases (asset-backed leases may be slightly lower, but 3.2% is defensible)

Auditor view: ✓ Easy pass. Observable, recent market rate.

Scenario 2: Mid-Cap Private Company, No Public Debt

Company: £50m revenue manufacturing company, privately held
Bank facility: £10m revolving credit facility at SONIA + 2.25% (current rate ~4.50%)
Lease term: 7 years (longer than bank facility)

Approach:

• Start with observed rate: 4.50% on the RCF
• Adjust for term: 7-year terms usually cost 0.30— 0.50% more than 3-year terms
• Adjusted IBR: 4.50% + 0.40% = 4.90%

Auditor challenge: ⚠️ Likely. Auditor will ask: "How did you determine the 0.40% adder? Show comparable data."

Better approach: Obtain a formal quote from your bank: "What would you charge for a 7-year asset-backed facility at this size?" Use that rate directly.

Scenario 3: Early-Stage Startup, High Risk

Company: 2-year-old tech startup, pre-revenue
Available debt: Only venture debt at 12% (very expensive)
Lease: Office space, 3-year lease at £100k/year

Approach: Venture debt at 12% is not representative of typical borrowing. Instead:

• Estimate credit spread for startups: typically 8— 12%
• Risk-free rate (3-year gilt): 2.8%
• Estimated IBR: 2.8% + 9% = 11.8%
• Round to 12% (conservative)

Auditor view: ✓ Reasonable. Must be supported by a brief memo explaining the estimate.

Implicit Rate vs. IBR: When Do You Use Each?

Implicit Rate: The discount rate that equates the PV of lease payments to the fair value of the asset. It's determined by the lessor, rarely given to the lessee, and usually not known.

When to use: Only if the lessor explicitly states it in the lease agreement. For example: "The lessor determines the implicit rate to be 4.5%." This is rare.

IBR: The rate the lessee estimates based on borrowing costs. Used for 99% of leases in practice.

Audit practice: Auditors will ask whether you attempted to determine the implicit rate. Even if unsuccessful, show that you tried (e.g., "We requested the implicit rate from the lessor; they did not provide it. Therefore, we used IBR."). This demonstrates you followed IFRS.

What Auditors Scrutinize (And Challenge)

Red Flag 1: IBR Is Lower Than Observable Borrowing Rates

Audit finding: "You claimed IBR of 3.5%, but your bank facility is at 6.2%. Explain the difference."

How to avoid: Document why your IBR differs from existing rates. For example:

• "Our RCF is at 6.2% because it includes a commitment fee and fronting fee on an unused facility. For asset-backed borrowing, the rate would be 4.8%."
• "Our bonds are at 3.2%, but leases are less creditworthy than secured bonds, so we add 0.5% for collateral risk: 3.7%."

Red Flag 2: IBR Doesn't Vary by Lease Term

Audit finding: "You used 5.0% for a 3-year lease and 5.0% for a 10-year lease. Long-term borrowing is more expensive. Why no variance?"

How to avoid: Document a rate curve. For example:

• 3-year leases: 4.8%
• 5-year leases: 5.2%
• 10-year leases: 5.8%

Derive this from gilt curves or comparable bond issuances.

Red Flag 3: No Supporting Documentation

Audit finding: "We asked for your IBR calculation; you provided none. How did you arrive at 5.5%?"

How to avoid: Build a one-page IBR policy documenting your methodology. Include:

• Date the policy was set
• Source of rates (e.g., "gilt yields as of 1 Jan 2026")
• Calculation (e.g., "Risk-free rate 2.5% + credit spread 2.0%")
• Supporting evidence (print-outs of gilt yields, bond prospectuses, etc.)

Building an IBR Policy

Here's a template:

Common IBR Errors (What Auditors Catch)

Error 1: Using Cost of Equity Instead of Borrowing Rate

❌ Wrong: "Our WACC is 8%, so IBR is 8%"

✓ Correct: "Our borrowing rate (cost of debt) is 5%. That's our IBR."

Cost of equity and WACC are far too high for a borrowing rate and will overstate lease liabilities.

Error 2: Not Adjusting IBR for Currency

❌ Wrong: Using a GBP-based IBR (3.5%) for a EUR lease, when EUR borrowing costs are 2.8%

✓ Correct: Adjust IBR by currency. EUR leases use EUR-based IBR (2.8%), USD leases use USD-based IBR (4.2%), etc.

Error 3: Forgetting to Update IBR Annually

❌ Wrong: Using the same 4.5% IBR in 2024, 2025, and 2026, even though interest rates have changed

✓ Correct: Review and update IBR annually (or when rates significantly change). New leases use current rates; existing leases use rates at lease commencement (not remeasured).

Error 4: Inconsistency Across Leases

❌ Wrong: Using 4.5% for one office lease and 5.5% for another nearly identical office lease

✓ Correct: Standardize rates. Similar leases (same term, currency, collateral) use the same rate. Document the policy.

Frequently Asked Questions

Real-Life Case Study: Setting the Incremental Borrowing Rate