# Credit Card Interest Calculator: Partial Payment Cost > Credit card interest calculator: the interest, GST and late fee on your next bill when you pay only part of it, and why interest runs on the full bill. Source: https://trykosh.com/tools/credit-card-interest-calculator Free tool - Loans and credit cards # Credit card interest calculator Pay anything less than the full bill and the interest-free period vanishes. See what carrying a balance adds to your next statement. Rules checked 25 October 2026Free - no sign-upRuns in your browser Charges on your next statement INR 3,352 on INR 40,000 left unpaid. That's 8.4% in one month Interest**INR 2,841** GST at 18%**INR 511** Yearly rate**43.2% (52.9% compounded)** Paid **INR 10,000**Carried forward **INR 40,000**Charges **INR 3,352** Interest on the full INR 50,000 for 40 days INR 2,367 Interest on the unpaid INR 40,000 for 10 days INR 473 GST on interest and fees INR 511 Total charges INR 3,352 Next statement opens at (before new spends) INR 43,352 Once you carry a balance, interest runs on the whole bill from each purchase date, not just on what you left unpaid, and new purchases lose their interest-free period until you clear it. ## Upload your statement and Kosh does this for you. Upload a bank or card statement and Kosh finds every EMI and card charge, then builds the fastest way out of debt that still fits your month. [Start free](/signup?via=tool-credit-card-interest-calculator) ## How the credit card interest calculator works Card interest is quoted per month, commonly around 3 to 3.75%, which is roughly 36 to 45% a year before compounding. There is no regulatory cap on card rates in India; in December 2024 the Supreme Court set aside an earlier 30% cap. The 3.6% default is illustrative: check your card's most important terms. The interest-free period applies only when you pay the full statement balance by the due date. If you pay part, interest is charged on the entire bill from each transaction date to the date you pay, and then on the unpaid balance until the next statement. That is why paying 80% of the bill doesn't cut interest by 80%. The calculator converts the monthly rate to a daily rate, charges it on the full bill for the days from purchase to payment, and on the unpaid part for the days to the next statement. GST at 18% is added to the interest and any fees. If you pay less than the minimum amount due, a late fee applies, usually in slabs by bill size. Under RBI rules, a late fee can be charged only if the account is overdue for more than three days, and only on the amount outstanding after the due date. Interest = bill x d x days to payment + unpaid x d x days to next statement; d = monthly rate x 12 / 365 GST 18% on interest and fees Minimum due commonly 5% of the bill, with a floor ## Worked example: Aman pays a quarter of his bill Aman's statement shows INR 80,000 after a holiday. He pays INR 20,000 by the due date, more than the minimum, so no late fee applies. At 3.75% a month, he is charged INR 3,452 of interest on the full INR 80,000 for 35 days and INR 888 on the unpaid INR 60,000 for 12 days. With INR 781 of GST his next statement carries INR 5,121 in charges and opens at INR 65,121 before any new spending. Charges on your next statement INR 5,121 on INR 60,000 left unpaid. That's 8.5% in one month Interest**INR 4,340** GST at 18%**INR 781** Yearly rate**45% (55.5% compounded)** Paid **INR 20,000**Carried forward **INR 60,000**Charges **INR 5,121** Interest on the full INR 80,000 for 35 days INR 3,452 Interest on the unpaid INR 60,000 for 12 days INR 888 GST on interest and fees INR 781 Total charges INR 5,121 Next statement opens at (before new spends) INR 65,121 Once you carry a balance, interest runs on the whole bill from each purchase date, not just on what you left unpaid, and new purchases lose their interest-free period until you clear it. [Load this example into the calculator ->](?bill=80000&paid=20000&rate=3.75&daysBefore=35&daysAfter=12#calculator) ## Good to know - Paying the full balance by the due date is the only way to avoid interest. Paying the minimum only avoids the late fee. - Once you revolve, new purchases also attract interest from day one until the whole balance is cleared. - Cash withdrawals on a card carry interest from the day of withdrawal plus a cash advance fee, with no interest-free period at all. - If you can't clear the bill, converting it to an EMI or taking a lower-rate personal loan to pay it off usually costs far less than revolving. ## Frequently asked questions How is credit card interest calculated? If you don't pay the full bill, interest is charged daily on each transaction from its date until you pay, and then on the unpaid balance. The monthly rate, often around 3.5%, is converted to a daily rate, and 18% GST is added to the interest. If I pay part of the bill, is interest only on the unpaid amount? No. Paying part of the bill means you lose the interest-free period on the whole bill, so interest runs on the full amount from each purchase date until your payment, and on the remainder after that. What is the annual interest rate on credit cards? A monthly rate of 3.6% is 43.2% a year simple, or about 52.9% once compounded monthly. Rates differ by card and issuer and are listed in the card's key terms. Is GST charged on credit card interest? Yes. Interest, late fees and other card charges attract 18% GST, which appears as a separate line on your statement. When is a late payment fee charged? When you don't pay at least the minimum amount due by the due date. RBI rules allow the fee only after the account is more than three days past due, and only on the amount outstanding after the due date. ## Sources and assumptions - [Reserve Bank of India](https://www.rbi.org.in/) - [CBIC GST portal](https://cbic-gst.gov.in/) Rules and rates last checked on 25 October 2026. Results are estimates for planning and education, not tax, legal or investment advice. Kosh is an educational financial planning tool by Primedepth Labs. It is not a SEBI-registered investment adviser and does not offer personalised investment advice, hold your money or execute trades. Markets carry risk; read scheme documents carefully and consult a registered adviser before acting.