Using this compound interest rate converter
- Enter the input rate as a percentage (for example, 6).
- Choose how that rate is compounded on the left (monthly APR, annual APY, daily, etc.).
- Choose the output compounding on the right — the equivalent rate appears instantly when you click Calculate.
- Use Save after calculating to store the conversion in your browser.
This tool focuses on rate conversion. To project balances with deposits, term, and charts, pair it with a full interest or investment growth calculator.
What is compound interest?
Compound interest earns returns on both the original principal and on interest that has already accrued. Each compounding period adds to the balance, so later periods calculate interest on a larger base. That snowball effect is why savings accounts, bonds, and loans quote both nominal rates and effective annual yields.
Periodic compounding formula
When interest compounds n times per year for t years at nominal rate r:
Continuous compounding
As compounding intervals shrink toward zero, the balance approaches the continuous model:
Rule of 72
A quick mental estimate for doubling time at a rough annual rate:
At 6% per year, money doubles in about 72 ÷ 6 ≈ 12 years. The shortcut is approximate — precise answers need the full exponent formula above.
Compounding frequency reference
| Frequency | Periods per year | Typical use |
|---|---|---|
| Annually (APY) | 1 | Quoted effective yield on savings |
| Quarterly | 4 | Some bonds and dividends |
| Monthly (APR) | 12 | Credit cards, many loans |
| Biweekly | 26 | Payroll savings plans |
| Daily | 365 | High-yield savings marketing |
| Continuously | ∞ | Theoretical upper bound |
Why rates look different
A 6% monthly nominal rate is not the same as 6% annual. Twelve monthly compounding periods produce about 6.17% effective annual yield — the default example on this page. Lenders and advertisers may quote whichever figure looks lower or higher, so converting to a common basis (usually APY) makes comparisons fair.
Examples and use cases
Worked example
Convert a 6% APR compounded monthly to an annual equivalent:
- Monthly periodic rate = 6% ÷ 12 = 0.5% per month
- Effective annual yield = (1 + 0.005)12 − 1 ≈ 6.17% APY
Real-world use cases
- Savings account shopping: Bank A quotes 4.8% APY while Bank B advertises 4.65% compounded daily — convert both to the same basis before choosing.
- Credit card comparison: A card lists 19.99% APR; converting to an effective annual rate clarifies the true yearly cost if you carry a balance.
- Investment due diligence: A fund prospectus mixes monthly and quarterly compounding — normalize rates to compare two bond or money-market products fairly.