Formula
Monthly interest formula
Monthly interest = balance x APR / 12; daily interest = balance x APR / 365The billing-cycle estimate uses a daily periodic rate, which is common for credit card interest estimates.
Monthly Interest Calculator
Use this monthly interest calculator to translate APR into estimated monthly, daily, and billing-cycle interest.
Planning estimate
Live calculator
Monthly interest
Monthly interest$95.79
Balance multiplied by APR divided by 12.
Billing-cycle interest$94.48
30 days using a daily periodic rate estimate.
Daily interest$3.15
Daily periodic rate is 0.0630%.
Monthly interest is an estimate
The monthly shortcut divides APR by 12. Many credit cards and some accounts calculate interest daily, so the billing-cycle estimate uses APR divided by 365 and multiplies by the number of days entered.
Interest rate conversion
Shows the monthly and daily rate used in the estimate.
| Measure | Estimate |
|---|---|
| APR | 22.99% |
| Monthly periodic rate | 1.9158% |
| Daily periodic rate | 0.0630% |
| Billing-cycle interest | $94.48 |
Use this as a planning estimate. Taxes, fees, rates, account terms, provider policies, local rules, and timing can change real-world results.
How to use
Steps
- Enter the balance.
- Enter the APR.
- Enter the number of billing days.
- Compare monthly interest, daily interest, and billing-cycle interest.
Example
Sample calculation
Balance$5,000
APR22.99%
Billing days30
Monthly interest$95.79
Calculator use
Best for
- Estimating affordability, payment, payoff, interest, APR, refinance, rent, or debt scenarios before a money decision.
- Comparing terms, rates, balances, fees, taxes, insurance, debt payments, or split shares with assumptions visible.
Before relying on it
Check first
- Treating an estimate as an approval, quote, credit decision, payoff statement, tax result, or legal payment obligation.
- Leaving out fees, escrow, insurance, property tax, PMI, minimum payments, compounding, promotional rates, or local rules.
- Comparing scenarios with different time horizons, upfront costs, credit assumptions, or one-time versus monthly costs.
Details
What to know before using the result
Monthly shortcutAPR divided by 12
This is a simple estimate for turning an annual rate into a monthly interest amount.
Daily periodic rateAPR divided by 365
Many card issuers use a daily periodic rate, so billing-cycle interest can depend on days and daily balances.
Balance methodAverage balance matters
Actual credit card interest can use average daily balance, daily compounding, grace periods, and different APRs for different balances.
Source notes
References used for this calculator
Benchmarks
How to read the result
APR / 12: Monthly shortcut.
Good for a quick monthly interest estimate.
APR / 365: Daily estimate.
Useful for billing-cycle interest when interest accrues daily.
Pay sooner: Less interest.
When interest accrues daily, reducing the balance earlier can reduce interest.
Calculator accuracy
Methodology and assumptions
Formula, inputs, limitations and review record
Formula
Monthly interest = balance x APR / 12; daily interest = balance x APR / 365
Inputs used
Balance, APR, Billing days
Limitations
Money results are planning estimates. Actual taxes, account terms, rates, fees, timing, local rules, and provider policies can change the real-world result.
Review record
Catalog QA baseline on June 6, 2026. This date marks the catalog-wide automated and editorial QA baseline, not a tool-specific expert review.
Cite this page
Toolkit Shelf. Monthly Interest Calculator. https://toolkitshelf.com/tools/monthly-interest-calculator
FAQ
Common questions
How do I calculate monthly interest from APR?
Divide APR by 12, then multiply the monthly rate by the balance.
How do I calculate daily interest?
Divide APR by 365 to estimate a daily periodic rate, then multiply by the balance.
Is credit card interest always monthly?
No. Many credit cards calculate interest daily, often based on average daily balance.
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