Project how savings and investments grow with compounding and regular monthly contributions, year by year.
Banks advertise savings accounts that compound “daily” and loans that compound “monthly”. Does it matter? Yes, but less than the marketing suggests. Here’s how compounding frequency works and how to compare offers fairly.
What compounding frequency means
The compounding frequency is how often earned interest is added to your balance so that it starts earning interest itself. The annual rate is divided into that many periods:
- Annually: once a year at the full rate
- Semi-annually: twice a year at half the rate
- Quarterly: four times a year at a quarter of the rate
- Monthly: twelve times at one-twelfth
- Daily: 365 times at 1/365th
The formula is A = P × (1 + r/n)^(n × t), where n is the number of periods per year.
The numbers
$10,000 at a nominal 6% for 10 years, with no further deposits:
| Compounding | Balance after 10 years | Effective annual rate |
|---|---|---|
| Annually | $17,908.48 | 6.000% |
| Semi-annually | $18,061.11 | 6.090% |
| Quarterly | $18,140.18 | 6.136% |
| Monthly | $18,193.97 | 6.168% |
| Daily | $18,220.29 | 6.183% |
| Continuous (theoretical limit) | $18,221.19 | 6.184% |
Going from annual to monthly compounding adds about $285 over ten years. Going from monthly to daily adds just $26. The gains shrink fast, and there’s a mathematical ceiling called continuous compounding.
APR vs APY (or AER / EAR)
Because frequency changes the real return, regulators require a standardised figure:
- APR (annual percentage rate): the nominal yearly rate, before compounding. Usually quoted on loans.
- APY (annual percentage yield), also called AER in the UK or EAR (effective annual rate): the rate you actually earn in a year after compounding. Usually quoted on savings.
APY = (1 + APR/n)^n − 1
A 6% APR compounded monthly is an APY of 6.168%. The compound interest calculator shows this effective rate for whichever frequency you choose, so you can compare a “5.9% compounded daily” offer against a “6% compounded annually” one on equal terms. In that case the daily offer’s APY is about 6.08%, so it wins.
Lenders like quoting the lower APR; savings providers like quoting the higher APY. Make sure you’re comparing the same kind of number.
What matters more than frequency
Compounding frequency is a small lever. The big ones are:
- The rate itself. Moving from 6% to 7% adds far more than switching annual to daily.
- Time. Ten extra years of growth dwarfs any frequency difference. See Compound vs Simple Interest: The Difference, With Examples for why starting early matters so much.
- Fees and taxes. A 0.5% annual fee cancels the benefit of daily compounding many times over.
Frequency on loans
For borrowers, more frequent compounding means you pay slightly more. Most amortizing loans compound monthly to match the payment schedule, which is what our loan calculator assumes. Credit cards usually compound daily on the outstanding balance, one more reason to clear them quickly.
Quick checklist when comparing accounts
- Compare APY/AER for savings and APR for loans.
- Check for fees and minimum balances that reduce the real return.
- Ask whether the rate is fixed or variable, and whether it’s a teaser rate that drops later.
- Use the Rule of 72 to quickly see how long each option takes to double your money.
Project how savings and investments grow with compounding and regular monthly contributions, year by year.