Effective Interest Rate Calculator
Convert a nominal annual rate to its effective annual rate (EAR) and back, for any compounding frequency: monthly, quarterly, daily, and more.
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How to use
Choose the direction of the conversion with the tabs. To find the effective rate, enter the nominal annual rate and select how often interest compounds (monthly, quarterly, daily, etc.). The calculator returns the effective annual rate (EAR) and the periodic rate applied each period. To go the other way, enter the effective annual rate and get the equivalent nominal rate for that compounding frequency.
Nominal vs. effective: why the same number means different costs
A nominal annual rate is just a periodic rate multiplied by the number of periods in a year — it ignores compounding. A '12% nominal, compounded monthly' loan actually charges 1% each month, and interest earned on interest makes the real annual cost higher than 12%. The effective annual rate (EAR) captures that: EAR = (1 + j/m)^m − 1, where j is the nominal rate and m the number of compounding periods per year.
With j = 12% and monthly compounding (m = 12), the periodic rate is 1% and the EAR is (1.01)^12 − 1 = 12.6825%. The gap grows with frequency: the same 12% nominal compounded daily (m = 365) gives an EAR of about 12.7475%. Two products advertising '12%' can therefore cost different amounts depending on how often they compound.
The reverse conversion answers a different question: given a true annual cost you are willing to accept (say 15% effective), what nominal rate with monthly compounding matches it? j = m × ((1 + EAR)^(1/m) − 1) = 12 × (1.15^(1/12) − 1) ≈ 14.06% nominal.
The classic trap: monthly rates quoted as if they were annual
Store credit, credit cards, and informal lenders often quote a monthly rate — '5% monthly' sounds small. Annualized correctly it is (1.05)^12 − 1 = 79.59% effective per year, not 60%. Simply multiplying a monthly rate by 12 always understates the true cost, and the higher the rate, the bigger the understatement.
The same applies to savings and investments, where the effective rate is often called APY (annual percentage yield). A certificate paying 6% nominal with monthly compounding yields 6.17% effective — the honest number to compare against other options. To project how a deposit grows over time at a given rate, try our interest calculator.
Whenever you see a rate, ask two questions before comparing: is it nominal or effective, and what is the compounding period? Only effective annual rates are directly comparable across products.
Comparing offers with different compounding frequencies
Suppose bank A offers a loan at 13.8% nominal compounded monthly and bank B at 14% nominal compounded semiannually. Converting both: A gives an EAR of 14.71%, B gives 14.49%. Despite the lower headline number, A is the more expensive loan. Converting everything to effective annual rates is the only reliable way to rank offers.
Note that the effective rate still excludes fees, mandatory insurance, and other charges. It corrects for compounding, not for total cost — for that, ask the lender for the total amount repaid or the regulated total-cost figure in your country. Use this converter as the first filter, then compare full costs among the finalists — and once you have the right rate, estimate your monthly payment with our loan calculator.
Frequently Asked Questions
What is the difference between nominal and effective interest rate?
The nominal rate is the periodic rate multiplied by the number of periods per year, ignoring compounding. The effective rate includes the interest-on-interest effect, so it reflects the true annual cost or yield. They only match when interest compounds exactly once a year.
Is APY the same as the effective annual rate?
Yes — APY (annual percentage yield) is the term banks use for the effective annual rate on deposits and savings. EAR and APY are calculated with the same formula.
How do I annualize a monthly rate correctly?
Use (1 + monthly rate)^12 − 1, not monthly rate × 12. A 2% monthly rate is 26.82% effective per year, not 24%.
Does a higher compounding frequency always mean a higher effective rate?
For the same nominal rate, yes: daily compounding yields more than monthly, which yields more than annual. The effect approaches a limit (continuous compounding, e^j − 1), so the jump from monthly to daily is small compared to the jump from annual to monthly.
Which rate should I use in a loan calculator?
Most loan calculators, including ours, expect the nominal annual rate and divide it by 12 to get the monthly rate. If a lender gives you an effective annual rate, convert it to nominal (monthly compounding) with this tool before entering it.
Does the effective rate include fees and insurance?
No. It corrects only for compounding frequency. Origination fees, mandatory insurance, and other charges increase the real cost beyond the effective rate — compare total amounts repaid for the full picture.