THE NUMORIX GUIDE
How to use the CD Calculator
Last reviewed September 14, 2026
What this calculator does
The certificate-of-deposit projection converts term months to years and applies FV = deposit x (1 + annualRate / n)^(n x years), where n is the selected compounding frequency.
Formula and method
The certificate-of-deposit projection converts term months to years and applies FV = deposit x (1 + annualRate / n)^(n x years), where n is the selected compounding frequency. Total interest is future value minus deposit; effective annual rate is (1 + rate/n)^n - 1; after-tax interest multiplies interest by one minus the entered tax rate.
Variables and inputs
Enter deposit, annual interest rate, CD term in months, compounding frequency of 1, 2, 4, 12, or 365, and tax rate. Deposit and results are dollars; term is months; rate and tax are percentages.
Worked example
For a $10,000 deposit at 4.5% for 12 months with quarterly compounding, n = 4 and future value is 10,000 x (1 + 0.045 / 4)^4 = about $10,457.65. Interest is about $457.65, effective annual rate is (1.01125)^4 - 1 = about 4.5765%, and at 25% tax after-tax interest is about $343.24.
How to interpret the result
The future value assumes the deposit remains until maturity and the quoted rate stays constant. After-tax interest is a simple reduction of modeled interest, not a complete tax calculation. A CD's liquidity and early-withdrawal terms can matter as much as the rate.
Common mistakes to avoid
Enter the term in months, not years. Do not compare nominal rate without considering compounding frequency or tax treatment. Do not assume the tax rate is withheld at maturity in the same way for every account or taxpayer.
Assumptions and limitations
The model excludes early-withdrawal penalties, renewal terms, state taxes, account fees, deposit insurance limits, variable rates, and the actual tax timing for interest income. It also treats the entire deposit as invested on day one.