Effective interest rate

Definition

The effective interest rate (EIR) is the internal rate that discounts a loan’s expected cash flows to its initial carrying value. It is used under FRS 102 and IFRS to recognise interest and arrangement fees smoothly over the life of the debt.

In plain terms

Rather than expensing a big upfront fee in month one, EIR accounting drips it across the term, giving a truer cost per period.

Why it matters for your company

It changes how debt cost hits your profit and loss. Your accountant applies it, but knowing it exists explains why the interest charge in your accounts differs from cash interest paid.

In practice

Picture a UK limited company drawing a term facility that carries an arrangement fee alongside the stated interest. Cash-wise, the fee is paid up front and interest is paid on whatever repayment schedule applies. For the accounts, though, EIR treatment takes that same total cost and spreads it smoothly across the life of the facility, so no single period looks artificially expensive or cheap.

The practical effect shows up when the finance team reconciles bank statements against the general ledger. The cash paid in a given month rarely matches the interest expense reported in the profit and loss account for that same month, because the expense line is following the effective rate, not the cash timing. Directors who expect the two to line up exactly are usually the ones who raise a query with their accountant — the mismatch is normal, not a sign of an error.

Common pitfalls

The most frequent confusion is treating the effective interest rate as something the lender charges — it is not a pricing figure at all, but an accounting mechanism applied after the loan terms are already fixed. Comparing a facility's EIR against a headline rate from a different lender therefore tells a company very little, since the two numbers are answering different questions.

A second pitfall is assuming EIR treatment changes what is actually owed. It does not: it only changes how the same total cost is allocated across reporting periods for presentation in the profit and loss account. Finance teams that lose sight of this sometimes chase a discrepancy that is purely a timing artefact of the accounting method rather than a real difference in the underlying obligation, and worth distinguishing from the related effective annual rate.