Credit Card Interest Calculator
If you've carried forward part of your credit card bill past the due date, this calculator shows how much interest you'll be charged on it, using the same daily periodic rate method Indian card issuers apply — plus the 18% GST charged on the interest itself. Enter your outstanding balance, your card's annual interest rate, and the number of days involved to see the result.
Fill in the form and select "Calculate" to see your results here.
What is the Credit Card Interest Calculator?
This calculator works out the interest charged on a credit card balance that has been carried over unpaid, using the daily periodic rate method that Indian card issuers apply to revolving balances. It also adds the 18% GST that banks are required to charge on the interest amount itself, so the total shown matches the two separate line items — interest and GST on interest — that appear on a real statement. It is a simplified, single-balance model: the section below on important factors explains exactly how it differs from what your issuer computes internally.
How to use this calculator
- Enter the outstanding balance — the portion of your bill that was not paid by the due date.
- Enter your card's annual interest rate (APR), stated on your card agreement or monthly statement.
- Enter the number of days the balance has been outstanding — typically the length of a billing cycle, or the number of days since your last full payment.
- Select "Calculate Interest" to see the interest for the period, the GST charged on it, the total interest payable, and the equivalent daily periodic rate.
Formula
This is the daily periodic rate method: the annual percentage rate (APR) is converted to a daily rate by dividing by 365, and that daily rate is applied to the balance for every day it remains unpaid. It is the method printed on Indian credit card statements, and it is meaningfully different from simply dividing the annual rate by 12 to get a "monthly" rate, because interest accrues by the actual day count rather than in fixed monthly blocks.
Example
Suppose you carry an outstanding balance of ₹20,000 on a card charging 42% per annum, for 30 days. The daily rate works out to 42 ÷ 365 ≈ 0.115%. Applying the formula: Interest = ₹20,000 × 0.115% × 30 ≈ ₹690.41. GST at 18% on that interest adds ≈ ₹124.27, bringing the total interest payable to ≈ ₹814.68. For context, this works out to a monthly-equivalent rate of about 3.5% (42 ÷ 12) — useful as a rough comparison, though issuers actually charge by the day, not the month. Enter your own balance, rate and day count in the calculator above for an exact figure.
Factors that affect the result
- Outstanding balance. Interest is charged only on the amount actually carried over unpaid — not on your full credit limit, and not on spends already paid off by the due date.
- Interest rate (APR). Indian card issuers typically charge 30%–42% p.a. on revolving balances, among the highest rates in consumer lending, which is why carrying a balance for long stretches is expensive.
- Number of days. Interest accrues by the actual day count. A balance carried for a full 30-day cycle costs roughly proportionally more than one carried for 10 days at the same rate.
- The grace period. If you pay your entire statement balance by the due date, most Indian cards charge zero interest during the grace period (typically 20–55 days from the transaction date). This calculator only applies once a balance has actually been carried past the due date — a bill paid in full attracts none of this interest.
- Average daily balance vs. a single balance. This is the main simplification in this tool: real issuers typically track your average daily balance across the billing cycle, since new transactions and payments change the balance day to day. This calculator uses one representative outstanding balance held constant over the chosen number of days, which is the standard simplified model used by comparison calculators. If your balance changed significantly during the period, your actual statement interest may differ from this estimate.
- GST. The 18% GST is charged on the interest amount, not on the principal balance, and is a real, separate line item mandated under India's GST law for financial services.
Frequently Asked Questions
Most Indian card issuers use the daily periodic rate method: they divide your card's annual percentage rate (APR) by 365 to get a daily rate, then apply that daily rate to your outstanding balance for every day it remains unpaid. In practice, issuers track this against your average daily balance across the billing cycle, since the balance can change as new transactions and payments post. This calculator uses a single representative outstanding balance over a chosen number of days as a simplified model of that math — useful for estimating interest on a known balance, though your actual statement may differ slightly if your balance moved during the cycle.
A quoted card rate of, say, 42% per annum sounds like it should translate to roughly 3.5% a month (42 ÷ 12). But issuers don't apply a flat monthly rate — they apply APR ÷ 365 every single day, including on days within a partial month, and interest is charged on any balance that carries over, not just new spending. Over a full billing cycle this daily accrual on the actual number of days involved can differ from a rough monthly approximation, which is why the daily periodic rate is the method actually printed on statements and used by issuers, not a monthly shortcut.
Interest charged by a bank or NBFC on a credit card balance is treated as a financial service charge under India's GST law, and financial services attract GST at 18%. This is why your statement shows GST as a separate line item calculated on the interest amount itself, not on your outstanding principal. This calculator adds the same 18% on top of the computed interest so the total interest payable matches what actually appears on a real statement.
Most Indian credit cards offer an interest-free grace period, typically 20 to 55 days, between the transaction and the payment due date, provided you pay your full statement balance by the due date. If you clear the entire bill on time, no interest is charged at all — the grace period only disappears, and interest only starts accruing, once you carry forward any unpaid balance to the next cycle. This calculator is only relevant to a balance that has been carried over past the due date; a bill paid in full incurs zero interest under this or any other method.
Credit card revolving interest, modelled here at the 30%–42% p.a. range typical of Indian cards, is among the most expensive retail borrowing available. The Credit Card EMI Calculator models a deliberately different, discounted rate (roughly 13%–24% p.a.) that issuers offer when you convert a large purchase or outstanding balance into a fixed EMI plan — a cheaper, structured alternative to letting the balance revolve at the full card rate. If you're carrying a balance you can't clear immediately, converting it to an EMI is usually far less costly than paying the standard revolving rate month after month. If you're only ever making the minimum payment on a revolving balance, the payoff can take years and cost several times the original balance in interest alone, since interest keeps compounding on whatever hasn't been repaid yet.
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Calculations are estimates based on the information entered and the daily periodic rate method described above. Actual issuer statements may use an average daily balance across the billing cycle rather than a single fixed balance, and may apply rounding or fee conventions specific to your card. Tax rules, including GST rates, can change. See our full disclaimer.