CD Interest Calculator
Enter your deposit details to see final balance, total interest, and a full growth breakdown.
Deposit Details
Growth Breakdown
| Period | Interest Earned | Balance | Total Interest |
|---|
How the Math Works
This calculator uses the standard compound interest formula:
Where the periodic rate is derived from the APY so the effective annual yield is always correct:
| A | Final balance at maturity |
| P | Principal (initial deposit) |
| APY | Annual Percentage Yield — the effective annual rate as a decimal (e.g. 4.50% → 0.045) |
| n | Compounding periods per year (365 daily, 12 monthly, 4 quarterly, 1 annually) |
| t | Term in years |
| r_period | Periodic rate — interest earned each compounding period; derived from APY, NOT APY÷n |
Why derive r_period from APY rather than dividing APY by n? Dividing APY by n and then compounding overstates earnings — it would imply an effective yield higher than the stated APY. Using (1 + APY)^(1/n) − 1 ensures that compounding n times per year produces exactly the APY.
Early Withdrawal Estimator
Model the net proceeds if you withdraw before maturity. Penalty structures shown are common industry examples — actual penalties vary by bank and are defined in your CD agreement.
Penalty is applied to the interest accrued at time of withdrawal, then deducted from the balance. If the penalty exceeds accrued interest, the difference may be deducted from principal at some institutions. Net proceeds shown assume principal is always returned minus any excess penalty.
Frequently Asked Questions
CD interest uses the compound interest formula A = P(1 + r/n)^(nt), where P is the principal, r is the annual periodic rate derived from the APY, n is the number of compounding periods per year, and t is the term in years. The calculator derives the periodic rate from the APY as r_period = (1 + APY)^(1/n) − 1, ensuring the stated APY is the actual effective annual yield regardless of compounding frequency.
APR (Annual Percentage Rate) is the nominal rate before accounting for compounding. APY (Annual Percentage Yield) is the effective rate after compounding — it reflects what you actually earn in a year. For example, a CD with 4.50% APR compounded daily has an APY slightly above 4.50%. Banks are required by Regulation DD to disclose APY, so most advertised CD rates are already APY figures. This calculator accepts APY as input.
More frequent compounding means interest is added to the principal more often, which slightly increases the total earned. For a given APY, the compounding frequency technically affects only the growth path, not the final annual yield (because APY already accounts for compounding). The difference in dollar terms between daily and monthly compounding on a typical consumer CD is usually small — a few cents to a few dollars per year on a $10,000 deposit.
Most CDs charge an early withdrawal penalty — commonly 3 months of interest for terms under 12 months, and 6–12 months of interest for longer terms. The exact penalty varies by bank and is disclosed at account opening. The early withdrawal panel in this calculator lets you model the net proceeds for a given penalty and withdrawal month. Actual penalties at your institution may differ; consult your CD agreement for exact terms.
This calculator models standard fixed-rate CDs using the compound interest formula with APY as the effective annual yield. It does not model variable-rate CDs, bump-up CDs, or no-penalty CDs that have their own rules. Results are estimates for planning purposes. Always verify with your financial institution before making account decisions.