A certificate of deposit (CD) is one of the safest ways to grow cash you will not need for a set period. You agree to lock up a deposit for a fixed term — anywhere from a few months to five years — and in exchange the bank pays a guaranteed interest rate, usually higher than a regular savings account. This calculator shows exactly what your deposit will be worth at maturity.
How CD returns are calculated
CDs quote an annual percentage yield (APY), which already accounts for compounding within the year. Your maturity value is simply your deposit grown at that APY for the length of the term. Because the rate is fixed when you open the CD, you know your exact return the day you deposit — there is no market risk and, at an FDIC-insured bank, your principal is protected up to $250,000 per depositor.
A worked example
Deposit $10,000 into a 12-month CD paying 4.50% APY and you will have $10,450 at maturity — a guaranteed $450 in interest. Choose a 5-year CD at the same 4.50% APY and, thanks to annual compounding, the balance grows to roughly $12,462, earning about $2,462. The longer term lets your interest earn interest, which is why multi-year CDs can meaningfully outpace short ones even at the same rate.
The trade-off: early withdrawal penalties
The catch is liquidity. If you cash out before the term ends, the bank charges an early withdrawal penalty — commonly three to six months of interest on shorter CDs and up to a year of interest on longer ones. That penalty can wipe out much of your earnings, so only deposit money you are confident you will not need until maturity.
Getting the most from CDs
- Compare APY, not the nominal rate — APY is the true annual return after compounding.
- Consider a CD ladder: split your money across several terms so a portion matures each year, keeping some cash accessible while capturing longer-term rates.
- Watch for rate environments — locking a long-term CD makes sense when rates are high and expected to fall.
- Verify the institution is FDIC-insured (or NCUA-insured for credit unions) so your principal is protected.
- Set a maturity reminder; many CDs auto-renew at whatever rate is current unless you act during the grace period.