How is CD interest calculated?

The deposit is compounded at the stated APY divided by the number of compounding periods per year, repeated for as many periods as fall within the term. A 10,000 deposit at 5.0% APY compounded monthly for 12 months grows to about 10,511.62, an interest gain of roughly 511.62.

Does compounding frequency make a big difference to CD returns?

It matters, but less than the APY itself. On a 5,000 deposit at 3.5% for five years, annual compounding is the least generous of the common schedules; switching the same rate to monthly compounding raises the effective annual yield by a small fraction of a percentage point, adding a modest amount to the final total.

What happens if I withdraw from a CD before it matures?

Most CDs charge an early withdrawal penalty equal to a set number of months of interest, commonly three to twelve months' worth depending on the term, which is deducted from the balance at the time of withdrawal. On a short-term CD closed early, that penalty can consume most or all of the interest earned so far.

Is CD interest taxable?

Yes, in the US it is taxed as ordinary income in the year it is credited, even on a CD with a term longer than one year where you cannot access the cash yet. The bank typically reports interest of 10 or more on a Form 1099-INT.

What is a good CD rate right now?

There is no fixed number that stays accurate for long since rates move with the broader interest-rate environment, but online banks and credit unions have generally offered noticeably higher CD rates than large national banks for the same term. Compare a handful of current offers for the term length you want rather than relying on a rate you saw months ago.

How much of my CD deposit is insured?

In the US, FDIC insurance (or NCUA insurance at a credit union) covers up to 250,000 per depositor, per institution, per ownership category. A CD deposit above that at a single bank is only insured up to the limit, so larger sums are often spread across separate banks or account types to stay fully covered.

CD & fixed deposit calculator

A certificate of deposit locks a sum away for a fixed term in exchange for a rate that is usually higher than an ordinary savings account, and the payoff for giving up access is entirely determined by three inputs: the deposit, the APY, and how often the interest compounds. This calculator turns those three numbers into a maturity value so you can see the actual dollars earned before you commit funds you cannot touch until the term ends.

What the maturity value actually tells you

The maturity value is the deposit plus every bit of interest credited and re-invested over the term, so it already answers the question 'what will I have in hand on the day the CD matures'. Subtracting the original deposit from that figure gives the interest earned, which is the number worth comparing against what the same cash would have earned sitting in a regular savings account over the same stretch of time.

A reasonable benchmark for a one-year CD in the current US rate environment sits somewhere in the mid-single digits, with online banks and credit unions typically posting the higher end of that range and large brick-and-mortar banks posting noticeably less. Anything advertised well above that range for a standard, federally insured CD is worth double-checking for a promotional catch, such as a short introductory window or a large minimum balance.

Compounding frequency changes the outcome less than the headline APY does, but it is not nothing. Moving the same nominal rate from annual to monthly compounding raises the effective yield by a small amount because interest starts earning interest sooner within the term, which is why two CDs advertising the same APY can still finish with slightly different dollar totals if one states an APY that already reflects daily compounding and the other does not.

Three CDs with different terms and compounding

A 10,000 deposit at a 5.0% APY compounded monthly for a 12-month term grows to about 10,511.62, meaning the CD earns roughly 511.62 in interest over the year. The effective annual growth rate for this deposit, accounting for the monthly compounding, works out to about 5.12%, slightly above the quoted 5.0% APY.

A 25,000 deposit at a 4.25% APY compounded quarterly for a 36-month term matures at about 28,380.53, an interest gain of roughly 3,380.53 over the three years, or an average of about 93.90 a month. Because the rate is locked for the full 36 months, that figure holds regardless of what happens to market rates in year two or three, which is the main trade-off against a savings account whose rate can move at any time.

A smaller 5,000 deposit at a 3.5% APY compounded annually for a five-year term reaches about 5,938.43, for interest of roughly 938.43. Annual compounding is the least generous of the three schedules for the same stated rate, so a saver comparing two five-year CDs at an identical 3.5% APY, one compounding annually and one compounding monthly, would find the monthly version pays a few dollars more purely from the compounding mechanics rather than a better underlying rate.

When the maturity projection stops holding up

The maturity figure assumes the rate never changes for the life of the CD, which is true for a standard fixed-rate CD but not for a bump-up or step-rate CD, where the yield is scheduled to change partway through the term. If your CD has either feature, treat this calculator's output as the minimum you will earn rather than the exact figure.

It also assumes no early withdrawal. Cashing out a CD before maturity almost always triggers a penalty, commonly a forfeiture of somewhere between three months' and a full year's worth of interest depending on the term length and the institution, which can wipe out most or all of the gain shown here if the withdrawal happens early in a short-term CD.

The calculator does not account for tax. In the US, interest credited to a CD is taxable income in the year it is earned, even for a multi-year CD where the cash is not accessible until maturity, so the after-tax return on a taxable CD held outside an IRA will be lower than the maturity value implies, more so for savers in higher tax brackets.

Rate environment, insurance limits and timing

CD rates track the federal funds rate fairly closely, since banks compete for deposits against the yield available on short-term Treasury bills and money market funds; when the Federal Reserve raises or cuts its target rate, newly issued CD rates typically move within weeks, though a CD you already opened keeps its original rate for the full term regardless of what happens afterward.

US bank CDs are insured by the FDIC and credit union CDs by the NCUA, both up to 250,000 per depositor, per institution, per ownership category; a deposit above that limit at a single bank is only partially protected, so savers with larger sums often split funds across institutions or ownership categories to stay fully insured.

Outside the US, the mechanics differ: in the UK, a fixed-rate bond or fixed savings account plays the same role as a CD and interest is generally paid gross with the saver responsible for reporting it against their Personal Savings Allowance, while deposit protection through the Financial Services Compensation Scheme currently covers up to 85,000 per person, per firm, a different limit and structure from FDIC coverage.

Frequently asked questions

How is CD interest calculated?: The deposit is compounded at the stated APY divided by the number of compounding periods per year, repeated for as many periods as fall within the term. A 10,000 deposit at 5.0% APY compounded monthly for 12 months grows to about 10,511.62, an interest gain of roughly 511.62.
Does compounding frequency make a big difference to CD returns?: It matters, but less than the APY itself. On a 5,000 deposit at 3.5% for five years, annual compounding is the least generous of the common schedules; switching the same rate to monthly compounding raises the effective annual yield by a small fraction of a percentage point, adding a modest amount to the final total.
What happens if I withdraw from a CD before it matures?: Most CDs charge an early withdrawal penalty equal to a set number of months of interest, commonly three to twelve months' worth depending on the term, which is deducted from the balance at the time of withdrawal. On a short-term CD closed early, that penalty can consume most or all of the interest earned so far.
Is CD interest taxable?: Yes, in the US it is taxed as ordinary income in the year it is credited, even on a CD with a term longer than one year where you cannot access the cash yet. The bank typically reports interest of 10 or more on a Form 1099-INT.
What is a good CD rate right now?: There is no fixed number that stays accurate for long since rates move with the broader interest-rate environment, but online banks and credit unions have generally offered noticeably higher CD rates than large national banks for the same term. Compare a handful of current offers for the term length you want rather than relying on a rate you saw months ago.
How much of my CD deposit is insured?: In the US, FDIC insurance (or NCUA insurance at a credit union) covers up to 250,000 per depositor, per institution, per ownership category. A CD deposit above that at a single bank is only insured up to the limit, so larger sums are often spread across separate banks or account types to stay fully covered.

Sources

FDIC, Deposit Insurance FAQs — States the standard FDIC deposit insurance amount of 250,000 per depositor, per insured bank, per ownership category, as published on fdic.gov.
Federal Reserve, Selected Interest Rates (H.15) — Publishes current and historical short-term interest rate data, including the federal funds rate that CD pricing tracks, updated regularly by the Federal Reserve Board.
IRS, Topic no. 403 Interest received — Confirms that interest credited on bank deposits, including certificates of deposit, is taxable in the year it is earned and reportable by the payer on Form 1099-INT for amounts of 10 or more.