CostOfLivingByState

Free calculator | Updated October 2026

Compound Interest Calculator: Watch Your Savings Grow

See how a starting balance and regular deposits grow at any rate, how much is your money and how much is interest, what it will be worth in today’s dollars, and how far ahead a better rate puts you than the 0.37% national average.

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Annual (APY for savings)

%

US average, last 10 years: 3.4%

After 20 years

You would have $113,919, worth $58,370 in today’s money.
You put in$70,000
Interest earned+$43,919
In today's dollars (at 3.4% inflation)$58,370
Final balance$113,919

At the national average savings rate (0.37%, FDIC, September 2026) the same savings reach $73,034: $40,886 less.

$113,919Year 1Year 20
At 4.0%At the 0.37% national average

Rates compound at the frequency chosen; additions at the end of each period unless set to the start. Inflation adjustment divides by (1 + inflation) for each year. Taxes on interest are not included.

The two things that matter most

Time and rate. Doubling the years more than doubles the interest, because interest earns interest. And the gap between a big bank paying close to nothing and an account paying a competitive rate compounds the same way: the chart shows your rate against the national average on the same deposits.

Beat inflation, not just zero

A balance can grow while its buying power shrinks. Prices rose 3.7% over the past year, so any savings rate below that loses ground in real terms. The “today’s dollars” figure shows the real result. For long-term retirement saving with an employer match, see the retirement calculator; to see what past prices are worth now, the inflation calculator.

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Frequently Asked

Compound Interest Calculator: questions answered

How does compound interest work?
Interest is added to the balance, and the next period's interest is paid on that larger balance, so growth accelerates. $10,000 at 5% a year compounded annually grows to $16288.95 after 10 years: $6288.95 of interest, against $5,000 if the interest were only simple interest on the original amount.
What is the compound interest formula?
For a lump sum, A = P(1 + r/n)^(nt), where P is the starting amount, r the annual rate, n the number of compounding periods a year and t the years. Regular deposits add a second term, C × ((1 + i)^N - 1) / i, with i the rate per deposit period and N the number of deposits. The calculator runs month by month, which gives exactly the same answer for any mix of compounding and deposit timing.
Does compounding frequency matter?
A little. At 5%, yearly compounding pays 5.00%, monthly 5.12% and daily 5.13% effective. The rate itself and how long you leave the money matter far more. Savings accounts usually quote the APY, which already includes compounding: enter the APY and choose yearly compounding to match it exactly.
What is a good savings rate right now?
The FDIC's national average savings rate is 0.37% (2026-09), and many big banks pay less. High-yield accounts at online banks and credit unions pay several times that. Over 20 years, $10,000 plus $200 a month grows to about $61k at the national average and about $96k at 4%.
What does 'in today's dollars' mean?
Future money buys less. The calculator divides the future balance by inflation over the same period, by default 3.4% a year, the US average over the last 10 years from the BLS CPI, so you can see what the balance would buy at today's prices. Savings earning less than inflation lose buying power even as the balance rises.
Should I add money at the start or end of each month?
Money added at the start of each period earns one extra period of interest, so it ends slightly higher (an 'annuity due'). Most bank and government calculators assume the end of the period, which is the default here; tick the box to switch.

Reader questions

Something this site doesn't answer?

Write to us. A person reads every message and we answer the ones we can, with the source cited. If your question would help other readers, we may publish an anonymised version, and we ask you first. Price-level figures here are a general reference for comparing states, not financial or relocation advice, so check your own move with a certified financial planner.

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