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Calculation details
Planning estimate only, not financial, tax, or legal advice. Verify assumptions and current rules before making decisions.
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What does this calculator estimate?
CD calculator: compute certificate of deposit interest and maturity value from deposit, rate, and term with compounding. Free, private, runs in your browser.
How this calculator works
Formula
Maturity value = deposit x (1 + rate / compound)^(compound x years); interest = maturity value - deposit.
Worked example
A $10,000 CD at 5% compounded monthly for 36 months matures at $11,614.72, earning $1,614.72 of interest.
Cite this tool
BoringToolsKit. “CD Calculator.” boringtoolskit.com/cd-calculator/ (reviewed August 2026). Free to reference in articles, syllabi, and answer posts with a link.
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Worked example: $10,000 at 4.50% compounded monthly for 24 months
Set the deposit to $10,000, the rate to 4.50%, compounding to monthly, and the term to 24 months. The calculator splits the nominal rate into 12 periods per year: 0.045 / 12 = 0.00375 per month. The exponent is 12 x 2 = 24 compounding periods. The maturity value is $10,000 x (1.00375)^24.
Working through the arithmetic: (1.00375)^24 = 1.093990, so the maturity value is $10,939.90. Subtracting the $10,000 deposit leaves $939.90 in interest over two years. Because 4.50% is a nominal rate compounded monthly, the effective annual yield is (1.00375)^12 - 1 = 4.5940%, which the calculator reports as APY = 4.59%. That distinction matters: a bank quoting '4.50% APY' means a different thing than '4.50% compounded monthly' here, since 4.50% APY already bakes the compounding in.
Change one input and the picture shifts. At the same 4.50% compounded quarterly, $10,000 for two years grows to $10,937.09 ($937.09 interest), $2.81 less than monthly because interest earns interest less often. Compounded annually it lands at $10,920.25 ($920.25). Over short terms the compounding-frequency gap is small; stretch to 10 years and annual vs monthly compounding at 5.00% separates by roughly $56 on a $20,000 deposit.
Edge cases and what the formula does not model
The validator rejects a non-positive term outright: months = 0 or a negative term returns the 'Check inputs' message, and so does a negative deposit or negative rate. At rate = 0% the math still runs and is honest about it: maturity value equals the deposit exactly, interest earned is $0.00, and APY prints 0.00%. That is a legitimate result, not an error, and it is a useful sanity test for any bank offer.
The single biggest real-world omission is that the formula assumes the deposit sits untouched for the whole term. There is no field for monthly additions, so dollar-cost averaging into a savings account is out of scope; it also assumes no withdrawals, no early-withdrawal penalty, and no balance tiers. A CD that pays 5.00% APY but slams you with 6 months of interest for early withdrawal is indistinguishable here from one with no penalty. The result assumes the APY stays constant for the term, which holds for a fixed-rate CD but not for a variable-rate or promotional product that drops after an intro period.
Taxes and inflation are also absent, and at realistic rates they dominate the picture. $10,000 at 4.50% for two years earns $939.90; taxed as ordinary income at 24% in a taxable account, the after-tax interest is about $714, roughly a 3.4% effective annual rate after tax. At 2.5% inflation, the real purchasing power gain on that $939.90 is closer to $480 in today's dollars. The calculator measures nominal growth; treat its output as a gross ceiling, not take-home value.