Methodology and accuracy
Every number on this site comes from a formula we will show you. Here they are, along with the conventions we follow and the limits of what a calculator can tell you.
- Regulation DD conventions
- Open formulas
- Client-side only
- At maturity
- $10,450.00
- Interest
- $450.00
Term length
$10,000.00 for 1 year, compounded daily. Runs in your browser.
Why this site exists
What we are
CD Calculator is a set of free calculators for certificates of deposit. There is no account system, no lead capture and no rate table we are paid to place at the top. The entire product is the arithmetic, done correctly, with the formula shown next to the result.
That matters more here than in most calculator categories, because CD marketing routinely mixes APY and nominal rates, quotes headline figures tied to minimum deposits you may not meet, and buries the renewal terms. A calculator that shows its working lets you check the offer rather than trust it.
We are not a bank, a broker or an advisor, and we do not sell CDs. Nothing on this site is financial, tax or investment advice.
The maths
Every formula we use
Compound interest (maturity value)
A = P(1 + r/n)^(nt)
Every growth calculation: the main CD calculator, rate, interest, return, APR and short-term pages.
Nominal rate to effective yield
APY = (1 + r/n)^n − 1
The APY calculator, and internally whenever a rate is entered as APR.
Effective yield to nominal rate
APR = n × ((1 + APY)^(1/n) − 1)
The APR calculator, and internally whenever a rate is entered as APY so compounding is not applied twice.
Annualised rate of return
Return = (A ÷ P)^(1/t) − 1
The return calculator, to make CDs of different lengths comparable.
Early withdrawal penalty
Penalty = P × r × (penalty months ÷ 12)
The penalty calculator. Charged as simple interest on principal, the standard bank structure.
Ladder blended yield
Blended APY = Σ (rateᵢ × amountᵢ) ÷ total
The ladder calculator, weighting each rung's rate by the dollars in it.
Conventions
The assumptions behind every calculation
APY follows Regulation DD (12 CFR 1030), the US rule governing how institutions disclose yields on deposit accounts.
Daily compounding uses a 365-day year, matching standard US bank practice rather than a 360-day convention.
Interest is assumed to remain in the CD and compound. Where a bank pays interest out monthly instead, actual earnings are lower and follow simple interest.
Early withdrawal penalties are modelled as N months of simple interest on principal — the most common structure, though some institutions use a flat fee or a percentage of principal.
All results are before tax. CD interest is taxable as ordinary income in the year it is credited.
Ladder calculations do not assume reinvestment of maturing rungs, so the figures shown are the ladder's first cycle only.
Worked through
The core calculation, step by step
A = P(1 + r/n)^(nt)
The compound interest formula that sits underneath every growth figure on the site.
- A
- Value at maturity
- P
- Principal — the opening deposit
- r
- Nominal annual rate as a decimal
- n
- Compounding periods per year
- t
- Term in years
Step by step
- 1
Convert the quoted rate to a decimal.
- 2
If it was quoted as APY, convert to the nominal rate first so compounding is applied once, not twice.
- 3
Divide the nominal rate by n.
- 4
Add 1 and raise to the power of n × t.
- 5
Multiply by the principal to get the maturity value.
- 6
Subtract the principal to isolate interest earned.
Limits
What this calculator cannot tell you
It cannot tell you a bank's current rate. Rates move weekly and are set per institution, per term and sometimes per balance tier. Every figure here depends on the rate you enter being the one you will actually receive.
It cannot tell you your exact penalty. Disclosures vary, and a minority of institutions use structures other than months-of-interest. The penalty calculator models the common case.
It cannot tell you your after-tax return, which depends on your marginal rate and your state. And it cannot tell you whether a CD is the right product for you — that is a question about your timeline and your alternatives, not about arithmetic.
For those questions, speak to a qualified financial professional and confirm all terms directly with your bank or credit union before depositing.
Formulas and content last reviewed . Bank rates change frequently — confirm current rates directly with your institution.
Security & privacy
Your numbers never leave your browser
Bank-standard formulas
Uses the same compound interest and APY conventions as banks under Regulation DD.
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Keep exploring
Explore the rest of the site
- CD CalculatorThe main compound-growth calculator — deposit, rate, term, maturity value.
- CD Interest CalculatorCalculate exactly how much interest your Certificate of Deposit earns — monthly, at maturity, and with daily compounding.
- CD Ladder CalculatorBuild a CD ladder rung by rung and see maturity dates, blended yield and total interest update live.
- CD Early Withdrawal Penalty CalculatorFind out exactly what breaking your CD early costs — and whether the penalty eats into your principal.
- Guides (31)Long-form explanations of how CDs work, compared against the alternatives.
- CD glossaryEvery term defined, with the formula attached wherever one applies.
- FAQ hubDirect answers to the questions people actually ask about CDs.
- Full sitemapEvery page on the site in one index, plus the XML sitemap.
Check the numbers yourself
Every formula above is live in a calculator on this site. Enter your own figures and compare the result against your bank's disclosure.