Quick answerA CD interest calculator projects the maturity value of a certificate of deposit from the opening balance, annual rate, term, and compounding frequency. It separates principal from interest earned.
How CD interest grows
A certificate of deposit usually earns interest on both the original deposit and previously credited interest. More frequent compounding adds interest to the balance sooner, although the difference can be small when the term is short or the rate is modest.
The quoted rate may be a nominal annual percentage rate or an annual percentage yield. APY already reflects compounding over one year, while nominal APR does not. Confirm which figure your bank provides before comparing the calculator result with an account disclosure.
Term length and early withdrawal
The term controls how long the deposit earns the stated return. Months are converted to a fraction of a year for the compound-interest formula. At maturity, the projected balance includes the opening principal plus accumulated interest.
Many CDs charge an early-withdrawal penalty, often expressed as a number of days or months of interest. This calculator models holding the deposit for the full entered term. A penalty, rate step-up, broker fee, or automatic renewal can change the amount actually received.
How to use this cd interest calculator
- Enter the deposit, annual rate, and term.
- Choose APY when the bank quotes annual percentage yield; choose nominal APR only when that is the stated rate.
- Add a marginal tax rate for a simplified after-tax illustration.
Formula and method
The rate stays fixed, interest remains in the CD, no early withdrawal occurs, and no fees or additional deposits apply.
CD growth example
A $10,000 deposit earning a 4.5 percent nominal annual rate compounded monthly for 12 months grows by applying 4.5 percent ÷ 12 each month. The projected maturity balance is about $10,459.40, so interest is about $459.40 before tax.
If 4.5 percent is the bank's APY instead, a one-year $10,000 deposit would earn $450 under the stated APY. That small difference illustrates why the rate type matters.
APY versus APR: compare the same CD deposit
When an account disclosure states APY, use APY mode. That annual yield already includes the effect of compounding, so selecting monthly compounding does not add another layer of interest in APY mode.
| Rate entry | Maturity balance | Interest earned |
|---|---|---|
| 5% APY | $10,500.00 | $500.00 |
| 5% nominal APR, monthly compounding | $10,511.62 | $511.62 |
| 5% nominal APR, annual compounding | $10,500.00 | $500.00 |
The nominal monthly calculation is 10,000 × (1 + 0.05/12)¹². These hypothetical rates illustrate the calculation; they are not current CD offers. Fractional-year projections use the stated formula and may differ from a bank’s daily accrual and crediting rules.
Keep the optional tax field at zero when comparing gross interest with a bank disclosure. The tax illustration reduces the assumed rate; it is not a calculation of the tax due on your return.
For fixed coupon payments and market yield, use the bond price and yield calculator. For income paid per share, use the dividend calculator.
Rate definition: CFPB Regulation DD, Appendix A: annual percentage yield.
Common mistakes to avoid
- Entering APY as a nominal APR and compounding it again.
- Ignoring an early-withdrawal penalty when planning to access the money before maturity.
- Assuming the promotional rate continues after automatic renewal.
- Comparing taxable interest with an investment return quoted after tax.
Accuracy and practical limits
The projection follows compound-interest mathematics for a fixed rate and balance. It excludes taxes, account fees, penalties, tiered rates, additional deposits, and institution-specific rounding. Use the bank's disclosure for the contractual maturity amount.
Primary references: Deposit insurance details and limits can change; verify them at the FDIC.
Frequently asked questions
Should I select APY or APR?
Most U.S. deposit products advertise APY. APY already reflects compounding; nominal APR requires a compounding frequency.
Does the result include an early withdrawal penalty?
No. Penalties vary by institution and product.
Is the tax figure exact?
No. It is an illustration based on the entered marginal rate; tax timing, jurisdiction, and account type can change the outcome.