Stable Numbers
APR ↔ AER Converter
Convert between nominal APR and effective annual rate (AER) with common compounding periods. See the equivalent monthly and daily rates. Include simple fee effects, copy a share link and download a CSV.
Fees (optional)
Only used to show fee effect. Does not change the core APR↔AER conversion.
Paid at the start, reduces net proceeds.
Added to the balance and repaid over the term in the demo below.
Used only for the fee effect demo below.
This is a simple approximation that treats an upfront fee as reducing net proceeds and a financed fee as increasing the amount outstanding, with level monthly repayments over the term. For formal APR disclosures use lender documentation.
Frequency is the number of compounding periods per year. APR is nominal per year, AER is the real return or cost after compounding. Daily rate is based on 365 days.
About this converter
APR is a nominal yearly rate that does not on its own tell you what happens when interest is applied during the year. AER is the effective annual rate after compounding has done its work. The gap between APR and AER depends on how often interest is added. With monthly compounding the AER will be a touch higher than the APR because each monthly slice earns interest on the interest already added in prior months.
Use APR → AER when a lender quotes a nominal APR with a compounding schedule and you want the true annual effect. Use AER → APR if you have an effective rate, for example from a savings account headline, and you want to find an equivalent nominal APR at a given compounding frequency so that you can compare like with like across products.
The optional fee section provides a simple illustration of how charges can shift the effective cost. An upfront fee reduces the cash you actually receive at the start. A financed fee increases the balance that accrues interest. The demo computes an approximate effective annual rate by comparing what you receive with what you repay over a chosen term using level payments. This is helpful for planning, but it is not a regulatory APR calculation. Always check the lender’s own figures for formal comparisons.
The monthly and daily equivalents let you estimate interest for short periods and compare products that quote different bases. Copy the share link to save a setup or send it to a colleague, and export a CSV if you need a record of the assumptions and outputs.
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