Credit Card Interest Calculator

Worked example

Example: $4,000 at 24% APR with $150/month accrues about $1,400 in interest before payoff in roughly 34 months—raising the payment to $200 cuts interest materially.

When to use this

• Estimating interest on a credit card balance at a stated APR.
• Comparing how much interest you save by raising the monthly payment.
• Checking a balance-transfer offer against staying on your current APR.
• Planning payoff before a promotional 0% period ends.

Common examples

• $3,500 balance at 22% APR paying $150/month → often 32+ months to payoff with about $1,300+ in interest if no new charges.
• $8,000 balance at 18% APR paying $400/month → payoff in under 2 years with materially less interest than minimum-payment schedules.
• $1,200 balance at 0% promo APR for 12 months paying $100/month → paid off before promo ends with no interest if no new purchases.
• $6,200 balance at 24% APR paying $250/month → payoff often stretches past three years without extra payments.
• $1,800 balance at 16% APR paying $200/month → paid off in under a year with far less interest than minimum payments.

Common mistakes

• Using the loan-fee APR calculator for revolving credit card balances.
• Using promotional 0% APR for the whole timeline when it expires in months.
• Forgetting cash-advance APRs differ from purchase APR.
• Ignoring annual fees outside the interest math.

How it works

Enter your credit card balance, APR, and either a fixed monthly payment, a target payoff timeline, or a minimum-payment rule (percent of balance with a floor). Optionally model a promo APR for N months, then continue amortization at a go-to APR until paid off.

Limitations

Assumes a fixed APR and steady monthly payment without new charges. Promotional rates, fees, and daily compounding may change real payoff timing.

Privacy and file handling

Your data stays on your device and is not uploaded.

Accuracy & methodology

This section documents how the calculator works, what it leaves out, and when results were last reviewed. Figures are educational estimates—not professional advice—and are not labeled "current" unless tied to automatically updated reference data.

Formula source or methodology

Iterative month-by-month balance reduction: interest on average daily balance approximation from APR, payment applied after interest, until paid off or horizon reached.

Jurisdiction

United States (generic revolving credit math)

Unit system

Currency; APR percent

Rounding method

Currency amounts round to two decimal places (half up via Math.round × 100 / 100).

Assumptions

• Fixed APR
• Fixed monthly payment
• No new purchases unless modeled

Known omissions

• Not tax, legal, investment, or lending advice. Confirm material decisions with qualified professionals.
• Issuer minimum payment rules, grace periods, and daily compounding nuances
• Promotional 0% APR windows and penalty APR

Test cases (automated)

• Positive balance and payment produce a payoff timeline

Version & last verified

Logic version 1.0. Content and formulas last verified 2026-07-24.

Important notice

Results are estimates for educational purposes and are not financial advice. Actual interest, fees, and payment policies vary by issuer. Consult a qualified financial professional for personal guidance.