Payment Calculator

Payment Calculator

There are two ways to think about paying off a debt, and this calculator does both. The first is the ordinary one: you know the term you want, and you need the monthly payment that clears the balance in that time. The second runs the other way and is far more useful for existing debt: you know what you can afford to pay, and you want to know how long it will take and what it will cost. That second mode is where credit card balances become clear. Paying the minimum on a card often means decades of payments and interest exceeding the original balance, while adding a modest fixed amount each month can cut the payoff period to a fraction. Switch between the two modes to see both sides of the same debt.

How this is calculated

In fixed-term mode the payment comes from the amortisation formula: M = P × r × (1+r)ⁿ / ((1+r)ⁿ − 1), with r the monthly rate and n the number of months.

In fixed-payment mode the same relationship is solved for n instead: n = −log(1 − P×r/M) / log(1+r). If the monthly payment is less than or equal to the interest accruing each month, there is no solution — the balance never falls, and the debt is mathematically permanent.

Worked example on $8,000 at 19.99%: paying $200 a month clears it in about 56 months with roughly $3,200 of interest. Paying $300 clears it in 32 months with about $1,600. Half again the payment, half the interest, and two years of your life back.

Why minimum payments are designed the way they are

Credit card minimums are typically set as a small percentage of the balance, often 1% to 3% plus that month's interest. Because the percentage applies to a falling balance, the required payment falls too, which stretches the payoff over an extraordinarily long period.

The practical fix is to fix the payment. Choose an amount above the current minimum and keep paying exactly that as the balance drops. This one change converts a shrinking-payment schedule into a fixed-payment one and typically cuts years off the term without any increase in what you pay this month.

Which debt to attack first

Mathematically, pay the highest interest rate first — it costs the most per dollar owed. This is the avalanche method and it minimises total interest.

Behaviourally, paying the smallest balance first produces a cleared debt sooner, which some people find far easier to sustain. This is the snowball method, and it costs a little more in interest in exchange for a higher chance of finishing. Run both here and see how large the difference actually is for your numbers — it is often smaller than expected, in which case the method you will actually stick to is the right one.

How to use the payment calculator

Pick your mode. Fixed term if you know how long you want to take. Fixed payment if you know what you can afford.
Enter the balance and rate. For a credit card, use the purchase APR from your statement — cash advance and balance transfer rates differ.
Compare two or three payment levels. The point of fixed-payment mode is the comparison. Add $50 or $100 and watch what happens to both the term and the total interest.

Frequently asked questions

Why does my chosen payment say “never pays off”?

If the payment is less than the first month’s interest, the balance grows instead of shrinking. Increase the payment above the monthly interest amount.

How long will it take to pay off my credit card?

Switch to fixed-payment mode and enter your balance, APR and what you can pay monthly. Paying only the minimum on a typical card balance often takes well over a decade; a fixed payment slightly above the minimum usually cuts that by more than half.

Should I pay off the highest rate or the smallest balance first?

Highest rate first costs less in total interest. Smallest balance first clears a debt sooner and is easier to sustain. Run both — for most people the interest difference is smaller than expected, and the method you will actually finish is the better one.

Does a balance transfer help?

It can, if the promotional rate is genuinely low and you clear the balance before it expires. Factor in the transfer fee, usually 3% to 5% of the amount, and be aware that new purchases on the card may not get the promotional rate. Enter the post-transfer balance including the fee here to see the real payoff.