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Interest Bench

What interest costs you, and what it earns you.

Calculators for the money questions that come down to compound interest: clearing a balance, growing a deposit, and what a mortgage decision adds up to over its term. Every page shows its formula and names its source.

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Interest paid over thirty years on a $300,000 mortgage, at 6 percent and at 7 percent Two curves of cumulative interest on the same $300,000 loan over the same thirty years. At 6 percent the total reaches $347,515.44. At 7 percent it reaches $418,524.05. The gap at the end is $71,008.61, which one percentage point costs on this loan. $0k $50k $100k $150k $200k $250k $300k $350k $400k $450k yr 10yr 20yr 30 7% 6%
One point on a $300,000 mortgage: $71,008.61 more interest over thirty years, computed by the library the calculators use.

3 calculators

Debt

What a balance costs to carry, and how long it takes to clear.

  • Credit card payoff How long a balance takes to clear, and the interest it costs.
  • Debt snowball Several debts at once. Snowball and avalanche, side by side.
  • Minimum payment What paying only the minimum costs, under both issuer formulas.

7 calculators

Mortgage

Recasting, releasing equity, and paying down early.

6 calculators

Savings

What a deposit grows to, and how long a pot lasts.

  • CD calculator What a certificate of deposit pays by maturity.
  • Savings withdrawal How long a pot lasts at a given monthly draw.
  • APY calculator What a rate is worth once compounding is counted.
  • Money market Growth on a variable rate, with the variability stated.
  • Savings goal What to put aside monthly to reach an amount by a date.
  • CD ladder Staggered maturities, compared honestly against one long term.

2 calculators

College

Saving for education costs that are years out.

  • Pell Grant An estimate from the Student Aid Index on your FAFSA summary.
  • 529 calculator What regular contributions grow to by the first tuition bill.

One percentage point, three places

The same single point of rate, moved on three ordinary balances. Every figure here is computed by the calculators above, from the formulas those pages show you.

  • A $300,000 mortgage over 30 years

    6% to 7%

    $71,008.61 more interest over the term

    $1,798.65 a month becomes $1,995.91

    Mortgage calculators

  • An $8,400 card balance at $250 a month

    22.9% to 23.9%

    $468.01 more interest before it clears

    4 years, 7 months becomes 4 years, 9 months

    Debt calculators

  • A $10,000 certificate for one year

    4.5% to 5.5% APY

    $100.03 more interest earned

    $449.99 of interest becomes $550.02

    Savings calculators

A point is a point. What it costs depends entirely on how much is borrowed and for how long, which is the reason this site exists: the rate on its own tells you almost nothing.

How this site works

Every calculator here shows the formula it used and cites the authority it follows, because a number you cannot check is a number you have to take on trust. Where a result depends on an assumption, the assumption is printed next to it rather than buried.

This site computes. It does not advise. You will not find a recommended option, a best choice, or a "you should" anywhere on it. What to do with a figure depends on things a calculator cannot see: what else you owe, what you have put by, and how steady your income is. The arithmetic is here so you can weigh that yourself.