How to use the CD Calculator
- Enter the deposit amount and the advertised interest rate.
- Enter the term in months — CDs typically run from 3 to 60.
- Select the compounding frequency shown in the disclosure, usually daily or monthly.
- Compare the APY line, not the nominal rate, when shopping between banks.
- Check the penalty estimate before choosing a term longer than your actual horizon.
How the calculation works
A CD is a fixed-term deposit: the bank commits to a rate and you commit to leaving the money alone. Interest compounds at the disclosed frequency, and because banks must advertise APY under Regulation DD, the APY is the only figure that lets you compare offers with different compounding conventions on equal terms. The gap between nominal and APY is small at these rates but real — 4.5% compounded daily is 4.602% APY.
Early withdrawal penalties are the defining constraint. Typical terms are 90 days of interest on a one-year CD and 180 days or more on longer terms, and the penalty can eat into principal if you withdraw early enough. That makes the CD's term a hard commitment in a way a savings account's rate is not, and it is the reason a slightly lower rate on a liquid account is often the better trade for an emergency fund.
Two structural strategies address the horizon problem. A ladder splits money across staggered maturities so something matures regularly, giving partial liquidity and averaging across the rate cycle. A no-penalty CD trades a modest rate reduction for the option to exit early. Both are worth considering whenever the alternative is guessing where rates will be in three years.
A = P(1 + r/n)^(nt); APY = (1 + r/n)ⁿ − 1; typical penalty = P × r × penalty days / 365Source: Regulation DD, 12 CFR Part 1030 (Truth in Savings) APY calculation rules; FDIC deposit insurance limits, 12 CFR Part 330.
Worked example
$10,000 in a 12-month CD at 4.5%, compounded monthly.
- Monthly rate = 4.5% ÷ 12 = 0.375%.
- A = 10,000 × (1.00375)¹² = $10,459.40.
- Interest earned = $459.40.
- APY = (1.00375)¹² − 1 = 4.594%.
$10,459.40 at maturity — $459.40 of interest and an APY of 4.594% against the 4.5% nominal rate.
Frequently asked questions
Are CDs insured?+
Yes, up to $250,000 per depositor, per insured bank, per ownership category at FDIC banks and NCUA credit unions.
What happens at maturity?+
Most CDs auto-renew at the then-current rate after a short grace period, which is frequently a worse rate. Set a reminder for the grace window.
Is CD interest taxable?+
Yes, as ordinary income in the year it is credited, even if you do not withdraw it. Long CDs generate taxable income before you see the cash.
What is a CD ladder?+
Splitting a sum across several maturities so one matures each year, giving regular access to cash while capturing longer-term rates on the rest.
Last reviewed September 1, 2026. We review this page whenever the underlying formula, tax year, published rate or standard changes.