How to Calculate CD Rate & Maturity Value
A Certificate of Deposit (CD) earns interest through compound interest — meaning interest accrues on both the original principal and all previously earned interest. The standard formula used by banks and financial institutions worldwide is the compound interest formula, also known as the CD maturity formula.
- A = Maturity value (final balance, including interest)
- P = Principal (initial deposit amount)
- r = Annual interest rate expressed as a decimal (e.g., 4.5% = 0.045)
- n = Number of compounding periods per year (12 = monthly, 365 = daily)
- t = Time in years
To find the effective APY (Annual Percentage Yield) — the real annualized return when compounding is factored in — a separate formula applies: APY = (1 + r/n)^n − 1. This formula is standardized in the United States by the Truth in Savings Act (Regulation DD) and is used by all federally regulated banks to disclose the true return on deposit accounts.
The total interest earned is simply the difference between the maturity value and the principal: Interest = A − P.
| Term | APY | Maturity Value | Interest Earned | Effective Yield |
|---|---|---|---|---|
| 3 months | 4.50% | $10,112.73 | $112.73 | 4.58% EFF |
| 6 months | 4.50% | $10,226.91 | $226.91 | 4.58% EFF |
| 12 months | 4.50% | $10,459.21 | $459.21 | 4.59% EFF |
| 12 months | 5.00% | $10,511.62 | $511.62 | 5.12% EFF |
| 24 months | 4.50% | $10,940.86 | $940.86 | 4.70% EFF |
| 36 months | 4.50% | $11,445.09 | $1,445.09 | 4.82% EFF |
| 60 months | 4.50% | $12,516.10 | $2,516.10 | 5.03% EFF |
| 12 months | 5.50% | $10,564.36 | $564.36 | 5.64% EFF |
Frequently Asked Questions
What is the difference between APY and APR on a CD?
APR (Annual Percentage Rate) is the nominal interest rate before compounding is considered. APY (Annual Percentage Yield) accounts for compounding frequency and reflects the true annual return. For a CD with a 4.50% APR compounded monthly, the effective APY is approximately 4.594% — meaning you earn slightly more than the stated rate due to intra-year compounding. Always compare CDs using APY, not APR.
Does compounding frequency significantly change CD earnings?
For typical CD terms (3–24 months), the difference between daily and monthly compounding is small but real. On a $10,000 CD at 5.00% for 12 months: monthly compounding yields $511.62 in interest, while daily compounding yields $512.67 — a difference of $1.05. Over longer terms (5+ years) at higher balances, the compounding gap becomes more meaningful. When comparing CDs, always verify both the stated rate and the compounding frequency.
What happens if I withdraw a CD early?
Most CDs impose an early withdrawal penalty if you access funds before the maturity date. A common penalty structure is 90 days of interest for terms under 12 months, and 150–180 days of interest for terms of 12 months or longer. Some no-penalty CDs exist but typically offer lower APY rates in exchange for the added flexibility. Always review the bank's specific penalty schedule before opening a CD.