Banks love to advertise “interest compounded daily”. It sounds much better than annual compounding — but how much difference does it actually make? Less than most people expect. Here are the real numbers.
Why frequency matters at all
The more often interest is added, the sooner it begins earning interest itself. With annual compounding, interest earned in January waits until December to be added. With monthly compounding, it is added at the end of January and starts earning in February.
Effective annual rate at a 5% nominal rate
| Compounding | Periods per year (n) | Effective annual rate |
|---|---|---|
| Annually | 1 | 5.0000% |
| Semi-annually | 2 | 5.0625% |
| Quarterly | 4 | 5.0945% |
| Monthly | 12 | 5.1162% |
| Daily | 365 | 5.1267% |
Going from annual to monthly adds about 0.12 percentage points. Going from monthly to daily adds only about 0.01.
$10,000 at 5%: 10 years and 30 years
| Compounding | After 10 years | After 30 years |
|---|---|---|
| Annually | $16,288.95 | $43,219.42 |
| Monthly | $16,470.09 | $44,677.44 |
| Daily | $16,486.65 | $44,812.29 |
Over 30 years, monthly compounding beats annual by about $1,458. Daily beats monthly by only about $135.
There is a limit: continuous compounding
If interest were added every instant, you would reach continuous compounding, with an effective rate of er − 1. At 5% that is 5.1271% — barely above daily’s 5.1267%. No matter how often interest compounds, the benefit cannot exceed this ceiling.
What matters more than frequency
- The rate. A 5.2% account compounded annually beats a 5.0% account compounded daily (5.20% vs 5.13% effective).
- The time. Every extra year adds far more than any change in frequency.
- Fees and taxes. A small monthly fee can wipe out the whole compounding advantage on a modest balance.
How to compare accounts
Ignore the compounding frequency and compare the APY (or effective annual rate). It already includes compounding, so two accounts with the same APY will produce the same balance after a year regardless of how often each compounds. See What Is APY?
For borrowers
Frequency works against you on debt. A credit card at 22% compounded monthly costs an effective 24.36% per year if the balance is not paid. The bigger the rate, the bigger the effect of frequent compounding.
Key takeaways
- More frequent compounding always helps savers, but with sharply diminishing returns.
- Annual → monthly is noticeable; monthly → daily is tiny.
- Compare accounts by APY, not by compounding frequency.
Test any frequency with the Compound Interest Calculator, or go straight to the daily, monthly, quarterly or annual calculator.