Effective Interest Rate (EIR) Calculator
Calculate the Effective Interest Rate (EIR) for any nominal rate and compounding frequency. Compare EIR across annual, monthly, daily and continuous compounding with charts.
About This Calculator
The Effective Interest Rate (EIR) Calculator helps investors, borrowers, and financial professionals compute the true annual interest rate after accounting for compounding effects. Unlike the nominal (stated) interest rate, EIR reveals the actual return on investments or the real cost of loans by factoring in how frequently interest compounds within a year.
EIR is calculated using the formula EIR = (1 + r/n)^n - 1, where r is the nominal annual interest rate and n is the number of compounding periods per year. For continuous compounding, the formula is EIR = e^r - 1. The calculator also displays the periodic rate and a comparison table showing how EIR changes across different compounding frequencies — from annual all the way to continuous compounding. In addition, you can enter a principal amount and term to see the actual final balance and total interest earned at the effective rate.
Whether you are comparing fixed deposit offers in India, evaluating credit card APRs in the US, or reviewing savings account AERs in the UK, this tool gives you the standardized effective rate needed for accurate comparison. The interactive chart visualizes how increasing compounding frequency affects your effective return, and the breakdown table shows EIR values side-by-side for every compounding frequency.
Regional Notes
India: The Reserve Bank of India (RBI) mandates that banks disclose effective interest rates on fixed deposits, recurring deposits, and loans. Use this calculator to verify FD rates quoted by SBI, HDFC, ICICI, and other Indian banks. For example, an SBI FD at 6.5% compounded quarterly gives an EIR of approximately 6.66%.
United States: The Truth in Lending Act (TILA) requires lenders to disclose APR and the effective interest rate. EIR helps compare credit card rates, mortgage APRs, and certificate of deposit (CD) yields accurately. A credit card with 18% APR compounded daily has an EIR of 19.56%.
United Kingdom: The Financial Conduct Authority (FCA) requires providers to show the Annual Equivalent Rate (AER) for savings accounts and the APR for loans. EIR corresponds closely to AER. A UK savings account at 5% compounded monthly yields an EIR of 5.12%.
Frequently Asked Questions
What is Effective Interest Rate (EIR)?
The Effective Interest Rate (EIR) is the actual interest rate earned or paid on a financial product after accounting for the effect of compounding over a year. Unlike the nominal (stated) rate, EIR reflects how often interest compounds — monthly, quarterly, daily, or continuously — giving you the true cost of a loan or the real return on an investment.
How is Effective Interest Rate calculated?
EIR is calculated using the formula EIR = (1 + r/n)^n - 1, where r is the nominal annual interest rate and n is the number of compounding periods per year. For continuous compounding, the formula is EIR = e^r - 1. For example, a nominal rate of 12% compounded monthly yields an EIR of 12.68%.
What is the difference between nominal rate and effective interest rate?
The nominal rate is the stated annual interest rate without accounting for compounding. The effective interest rate includes the effect of compounding, showing the true annual return or cost. For example, 12% nominal compounded monthly gives 12.68% EIR, while compounded daily gives 12.75% EIR.
Why is effective interest rate higher than nominal rate?
EIR is higher than the nominal rate because compounding means interest earns interest multiple times per year. The more frequently interest compounds, the higher the effective rate. Daily compounding produces a higher EIR than annual compounding for the same nominal rate due to the compounding effect.
How does compounding frequency affect the effective interest rate?
Higher compounding frequencies result in a higher EIR. For a 12% nominal rate: annual gives 12.00%, semi-annual gives 12.36%, quarterly gives 12.55%, monthly gives 12.68%, weekly gives 12.73%, daily gives 12.75%, and continuous gives 12.75%. The difference becomes more significant at higher rates.
What is continuous compounding?
Continuous compounding is the theoretical limit where interest is calculated and added an infinite number of times per year. The formula is EIR = e^r - 1, where e is Euler's number (approximately 2.71828). It produces the highest possible effective rate for a given nominal rate.
How is effective interest rate used in India, US, and UK?
In India, RBI requires banks to disclose EAR on fixed deposits and loans for transparency. In the US, the Truth in Lending Act requires lenders to disclose APR and effective rates for credit cards and mortgages. In the UK, the FCA requires lenders to quote Annual Equivalent Rate (AER) for savings and APR for loans, which correspond closely to EIR.
How can I use the EIR to compare investment returns?
Always compare effective interest rates rather than nominal rates when evaluating different financial products. The calculator shows EIR across all compounding frequencies side-by-side, so you can identify which product truly offers the best return or lowest cost regardless of how often interest compounds.