Finance

Personal Credit Card Monthly Interest Calculator (30 Years)

Estimate monthly interest on a card balance. This personal version uses a 30-year planning term as its starting point.

The "Monthly interest" figure is the amount charged in interest for one month on the balance you entered, before any part of the balance itself is repaid, so paying only that amount leaves the balance unchanged.

Formula

Monthly interest equals balance times annual rate divided by 100 divided by 12.

How it works

Paying only interest leaves the balance unchanged. Paying more than interest reduces the balance.

Worked example

Balance $5,000.00, annual rate 18%, term 30 years. First, the monthly interest is $5,000.00 times 18 divided by 100 divided by 12, which is $900.00 divided by 12, which is $75.00. Over 360 months, paying only interest costs $75.00 times 360, which is $27,000.00. That is 540.0% of the balance. If only interest is paid, the balance at the end is still $5,000.00, because no part of the $75.00 payment repays the balance itself.

Who this term suits for a person: A 30-year term suits a person comparing a card balance with a mortgage-length horizon, for example someone who realises they have paid card interest for as long as a house loan lasts. Thirty years of $75.00 a month is $27,000.00, more than five times the balance, and no house, car, or asset was bought with that $27,000.00, it was only the cost of leaving $5,000.00 unpaid.

FAQs

Why is card interest high?
Card rates are usually higher than loan rates, so balances grow quickly if only minimum payments are made.

Is this personal calculator exact?
No, it is an estimate for planning only, based on the numbers you enter.

Are these figures financial advice?
No, they are estimates for planning only, not financial advice. Check with a qualified adviser for decisions involving large sums.

Is $27,000.00 of interest over 30 years really possible on $5,000.00?
Yes, on the page formula. Monthly interest is $75.00, and 360 months times $75.00 is $27,000.00, which is 540.0% of the balance. It sounds impossible only because people expect interest to stop once it passes the borrowed amount, but interest-only payments have no such stop.

What is a person trading when they carry a card balance for 30 years?
They are trading $27,000.00 of future spending power for the use of $5,000.00 that was never repaid. That $27,000.00 could have been savings, a deposit, or debt-free spending, but instead it went to interest while the $5,000.00 remained owed.

How can the $27,000.00 total be cut?
Only by cutting the balance or the rate, or both. Paying more than $75.00 a month reduces the balance and then reduces future interest. A lower rate reduces the monthly figure, for example 10% gives $41.67 a month. Stopping new card spending is also essential, or the balance will rise again.

Estimates only, not financial advice. Figures are approximate and do not include all fees, taxes, or changing rates unless stated.