CD Calculator

Estimate CD growth with APY or APR, review the formulas, and compare gross return with an after-tax estimate.

CD details

Model one certificate of deposit at a time. Results update as soon as the inputs are valid.

Initial deposit

Annual interest rate

Enter the quoted annual rate.

Rate type

APY (effective annual yield)

Best when the quoted rate already reflects a full year of compounding.

APR / nominal annual rate

Use this when the quoted rate needs a compounding frequency to determine actual growth.

Deposit length

Years

Months

Results

The output stays directly below the form so the page remains easy to scan on both desktop and mobile.

End balance

$11,576.25

Interest earned

$1,576.25

Equivalent APY

Deposit length

3 years

Balance mix

Principal and gross interest at maturity.

Growth by year

Each bar stacks the original principal and the accumulated interest at that point in time.

Variables in this scenario

Principal (P)

$10,000

Quoted annual rate

5% APY

Total time (t)

3 yr

Effective annual yield

Time in years

t = 3 + \frac{0}{12} = 3

Rate handling

y = 0.05,\quad APY = y = 0.05

End balance

A = P(1 + y)^t = 10000(1 + 0.05)^{3} = 11576.25

Interest earned

I = A - P = 11576.25 - 10000 = 1576.25

What a CD calculator helps you estimate

A certificate of deposit (CD) calculator estimates how much a lump-sum deposit can grow over a fixed term. It answers the questions most savers care about:

How much will the CD be worth at maturity?
How much of that ending balance is interest?
How does the answer change if the quoted rate is APY instead of APR?
How much of the return might remain after tax?

Because a CD usually has one deposit, one quoted annual rate, and a known term, the math is straightforward once the rate convention is clear.

APY vs. APR

APY and APR are both annual rates, but they do not mean the same thing.

APY already includes the effect of compounding over a full year. If a bank quotes a CD at 5.00% APY, that means one year in the CD turns $10,000 into$ 10,500 before tax.
APR is a nominal annual rate. You also need the compounding frequency to know the true yearly growth.

In most CD cases, APY is the better input because it reflects the actual annual yield the bank is advertising. If your bank only publishes APR, you can still use it by selecting APR / nominal annual rate and choosing the matching compounding frequency.

To convert APR to APY:

\text{APY} = \left(1 + \frac{\text{APR}}{n}\right)^n - 1

To convert APY back to APR for a given compounding frequency:

\text{APR} = n\left((1 + \text{APY})^{1/n} - 1\right)

Here, $n$ is the number of compounding periods per year: 1 for annual, 2 for semiannual, 4 for quarterly, 12 for monthly, and 365 for daily compounding.

If you need to convert between APR and APY outside the context of a CD, our dedicated APR to APY calculator lets you explore the relationship in more detail.

How CD growth is calculated

Let:

$P$ = initial deposit
$A$ = ending balance
$I$ = interest earned
$t$ = time in years
$r$ = APR as a decimal
$y$ = APY as a decimal
$n$ = compounding periods per year

If the rate is entered as APY:

A = P(1 + y)^t

If the rate is entered as APR with discrete compounding:

A = P\left(1 + \frac{r}{n}\right)^{nt}

If the rate compounds continuously:

A = Pe^{rt}

In every case, interest earned is:

I = A - P

This is why compounding frequency matters so much for APR input. The same nominal rate produces different outcomes when interest compounds annually, monthly, or daily.

How to use this calculator

Enter the initial deposit.
Enter the quoted annual rate.
Choose APY if the rate already represents the effective yearly yield.
Choose APR if the rate is nominal, then pick the compounding frequency.
Enter the deposit length in years and months.
Optionally add a marginal tax rate to estimate tax drag and after-tax return.

The result area shows end balance, interest earned, an ending-balance mix chart, and a year-by-year growth chart. The calculation steps section below the calculator also rewrites the active formula using your current inputs, which makes it easier to audit the math instead of treating the tool like a black box.

What makes this calculator different

It is APY-first, which matches how many banks actually quote CD rates.
It can switch to APR mode and show the equivalent APY when compounding matters.
It keeps the input on top and the result directly below it, which is easier to scan than a squeezed side-by-side layout.
It includes a concise formula walkthrough, not just a final number.
It adds an optional after-tax view so you can compare gross return against estimated take-home return.