How to Calculate CD Interest Rate and Maturity Value (Step-by-Step Math)
Regulation DD (12 CFR Part 1030, Appendix A) standardizes APY across U.S. banks. Three formulas cover most CD questions:
- Future value compound interest:
A = P × (1 + r/n)^(n × t) - Direct APY maturity:
A = P × (1 + APY)^(Months ÷ 12) - APY conversion:
APY = (1 + r/n)^n − 1
| $25,000 deposit | Rate | Interest | Maturity |
|---|---|---|---|
| 6-month | 4.40% APY | $544.08 | $25,544.08 |
| 12-month | 4.40% APY | $1,100.00 | $26,100.00 |
| 12-month (FDIC avg) | 1.70% APY | $425.00 | $25,425.00 |
| 18-month | 4.40% APY | $1,668.02 | $26,668.02 |
| 60-month | 4.40% APY | $6,005.77 | $31,005.77 |
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Frequently Asked Questions
How do I calculate CD interest rates and maturity value?
Use A = P × (1 + APY)^(Months ÷ 12). $25,000 at 4.40% APY for 12 months returns $26,100.00, or $1,100.00 of interest.
What is the difference between CD interest rate (APR) and APY?
The stated rate ignores compounding; APY includes it. A 4.50% stated rate compounded daily equals 4.60% APY.
Is a CD better than a high-yield savings account right now?
Only if savings rates average below the CD rate over the term. The Fed's range is 3.75%–4.00% after a September 2026 hike, so short terms or a ladder limit lock-in risk.
Can an early withdrawal penalty reduce my original CD principal?
Yes. A 3-month penalty of $269.38 on a $25,000 CD exceeds the $180.06 earned by month 2, returning $24,910.68.
Do I pay taxes on CD interest every year or only when the CD matures?
One-year-or-shorter CDs are generally taxed when paid; longer CDs generally require annual reporting of accrued interest (IRS Publication 550).
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Educational tool, not financial, tax, or legal advice. Your bank's disclosure controls actual rates, day counts, and penalties.