Annual Interest To Monthly Calculator
Convert between annual and monthly interest rates in both directions, with the nominal-vs-effective distinction most tools skip. Annual to monthly gives the simple rate, the compounded rate, and the daily periodic rate credit cards use. Monthly to annual gives the nominal (APR-style) and effective (APY-style) rates. To see how the effective rate compounds over time, use the effective interest rate calculator.
Rates only; fees are not included. The APR on a loan offer always exceeds the note rate because it folds in fees.
Quick Answer
Annual rate 12%: simple monthly 1.0000%, compounded monthly 0.9489%, daily periodic 0.032877%. The other way, monthly 1%: nominal annual 12.0000%, effective annual 12.6825%. The tool below reproduces all five figures.
Worked example, checked against this exact tool
Type 12% into the annual-rate field and click Calculate. The tool shows three monthly figures side by side. The simple monthly rate is 1.0000%, which is just 12 divided by 12. The compounded monthly rate is 0.9489%: slightly lower, because twelve months of compounding at this rate rebuilds exactly 12% over the year. The daily periodic rate is 0.032877%, which is what a credit card statement uses when it quotes a daily rate.
Now flip it: enter 1% as the monthly rate. The nominal annual rate is 12.0000% (1% x 12, no compounding). The effective annual rate is 12.6825%, because each month’s interest itself earns interest the following months. The gap between 12.00% and 12.68% is the cost of compounding, and it is the number lenders must disclose as the APR.
The formulas
Simple monthly = annual ÷ 12. Compounded monthly = (1 + annual)1 ÷ 12 − 1. Nominal annual = monthly × 12. Effective annual = (1 + monthly)12 − 1. Daily periodic = annual ÷ 365. The effective formulas are the same compounding math banks use to turn a nominal rate into an APY.
Which monthly rate should you use?
Use the simple monthly rate when a lender quotes an APR and applies a monthly periodic rate: standard practice for US credit cards. Use the compounded monthly rate when comparing investment returns quoted as effective annual rates and you want the matching monthly growth step. Twelve periods of 0.9489% multiply out to exactly 12%: compounding does part of the work, so the compounded figure is always slightly lower.
Nominal vs effective: the name game
Nominal annual (monthly × 12) is the APR-style quote; effective annual is what compounding actually delivers. In the US the effective rate on savings is called APY; in the UK it is AER. A 1%/month card is 12% nominal but 12.68% effective: the 0.68 points are the price of monthly compounding. For a deeper look at the true yearly cost including compounding, compare with the APR per month and real interest rate calculators.
What competing calculators miss
Most rate converters show one monthly figure and never say which convention it uses, so users silently mix APR-style and effective figures. This page shows both monthly rates side by side, converts both directions, and adds the daily periodic rate that credit cards actually apply to balances.
Frequently asked questions
How do you convert an annual rate to monthly?+−
Divide by 12 for the simple (APR-style) monthly rate, or use (1 + annual)^(1/12) – 1 for the compounded monthly rate.
How do you convert a monthly rate to annual?+−
Multiply by 12 for the nominal (APR-style) annual rate, or use (1 + monthly)^12 – 1 for the effective annual rate.
What is the daily periodic rate?+−
The annual rate divided by 365: the rate credit card issuers actually apply to daily balances. 18% APR = 0.0493%/day.
Is the effective rate the same as APY?+−
For deposits, yes: APY is the regulated name for the effective annual rate including compounding. For loans, the comparable concept is the effective rate, not the APR.
Can the effective rate be lower than the nominal rate?+−
No, with positive rates and compounding at least annually: effective is always equal to or higher than nominal.
Which rate do mortgages use?+−
US mortgages quote a nominal APR but accrue interest monthly on the balance: the payment math uses the monthly periodic rate (APR/12).
Why is the compounded monthly rate lower than annual/12?+−
Because compounding does part of the work: twelve periods of 0.9489% multiply out to exactly 12%, so each period can be smaller than 1%.
What is a good monthly interest rate?+−
Context-dependent: under 0.5%/month is cheap borrowing; credit cards run 1.5-2.5%/month. Compare effective annual rates, not monthly figures.
Does the calculator include fees?+−
No: it converts rates only. The APR on a real loan offer exceeds the note rate because fees are folded in.
How do I compare rates with different compounding?+−
Convert everything to effective annual rate (or APY): it is the only figure that makes different compounding schedules directly comparable.
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References
- CFPB: What is the difference between a loan interest rate and the APR? – Consumer Financial Protection Bureau (accessed 2026-10-17)
- CFPB: What is a Truth-in-Lending disclosure for an auto loan? – Consumer Financial Protection Bureau (accessed 2026-10-17)
- CLIMB: What Is APR and How Is It Calculated? – CLIMB (accessed 2026-10-17)
- CLIMB: What Is APR? How It Works and Why It Matters – CLIMB (accessed 2026-10-17)
- Cash1: What Is Apr (Annual Percentage Rate)? – Cash1 (accessed 2026-10-17)
- Axos Bank: What Is APY? How Annual Percentage Yield Works – Axos Bank (accessed 2026-10-17)
- SuperMoney: Simple vs. Compound Interest in Savings Accounts – SuperMoney (accessed 2026-10-17)
- Savings Interest Calculator: What Is APY? – Savings Interest Calculator (accessed 2026-10-17)
- 1st Bank: APY vs. Interest Rate Savings Account: Which is Right for You? – 1st Bank (accessed 2026-10-17)
- PrimeRate: How Compound Interest Grows Your Savings Over Time – PrimeRate (accessed 2026-10-17)