Definition
Interest rate is the price of borrowing (or return on lending) expressed as a percentage over a time period. Make sure rates are compared on consistent bases (APR vs APY).
Measured as
Measure Interest Rate with the same date, unit basis, and accounting or policy definitions used in the rest of your model.
Operator takeaway
- Tie Interest Rate to the same balance-sheet date, scenario, and decision memo you are using elsewhere in the model.
- Document which claims, costs, or adjustments your team includes before comparing numbers across forecasts, covenants, or valuation work.
Next decision
- Quantify the impact with APR to APY Calculator if you need to turn the definition into an operating assumption.
- Read APR vs APY: how compounding changes the effective rate if the decision depends on interpretation, policy, or trade-offs beyond the raw formula.
Where to use this on MetricKit
Calculators
- APR to APY Calculator: Convert APR to APY (and APY to APR) given compounding frequency.
- Loan Payment Calculator: Compute monthly payment, total interest, and total paid for a loan using amortization.
- Real Return (Inflation-adjusted) Calculator: Convert nominal return into real return given an inflation rate (and compare the difference).
- Convertible Note Conversion Calculator: Estimate how a convertible note converts in a priced round with interest plus a valuation cap and/or discount (simplified).
Guides
- APR vs APY: how compounding changes the effective rate: A practical guide to APR vs APY: what each means, how to convert between them, and common comparison mistakes.
- Loan amortization: how monthly payments and total interest work: A practical guide to loan amortization: monthly payment formula, why interest dominates early, and how term and rate affect total interest.
- Real vs nominal return: inflation-adjusted performance: A practical guide to real return: how inflation changes purchasing power and why nominal returns can mislead over long horizons.
- Convertible note: interest, cap/discount, and conversion basics: A practical guide to convertible notes: how interest accrues, how caps and discounts affect conversion price, and common modeling pitfalls.
- Interest expense: definition, formula, and how to calculate: Interest expense explained: what it is, the formula, how to calculate it, and how net interest expense works.