CD Interest Calculator
This CD interest calculator estimates the total balance and interest earned on a certificate of deposit, based on your initial deposit, term length, APY, and compounding frequency.
Also known as: CD interest calculator, CD calculator, certificate of deposit calculator, CD yield calculator, CD maturity calculator.
Balance = P × (1 + r ÷ n)^(n × t)Why Use a CD Interest Calculator Before You Open an Account
Banks advertise CDs by their APY, but that single percentage doesn’t tell you the actual dollar amount you’ll walk away with at maturity. Because compounding frequency, term length, and your initial deposit all interact, a CD interest calculator has to run the compound-interest formula for you rather than leaving you to compare rates as flat percentages.
This matters most when you’re comparing offers from different banks side by side. A 4.5% APY on an 18-month CD and a 4.3% APY on a 2-year CD aren’t directly comparable just by looking at the rate, since the term length changes how much time your money has to grow. As a result, running both scenarios through the same calculator gives you an actual dollar figure to compare rather than two percentages that are hard to weigh against each other.
Since interest earned on a CD is taxable income in the year it’s credited (even though you can’t touch it until maturity), this calculator also lets you enter a marginal tax rate to see an approximate after-tax figure alongside the before-tax number.
How This CD Interest Calculator Works
A certificate of deposit grows through compound interest, where the interest earned in each compounding period is added to the balance before the next period’s interest is calculated.
The formula
Balance = P × (1 + r ÷ n)^(n × t), where P is your deposit, r is the APY as a decimal, n is the number of compounding periods per year, and t is the term in years.
APY vs. APR
Because CDs are almost always advertised in APY, which already accounts for compounding, you generally don’t need to convert from APR before using this calculator.
Compounding frequency
More frequent compounding (daily vs. annually) produces a slightly higher return for the same stated APY, since interest starts earning interest sooner.
What this doesn’t include
Early withdrawal penalties, FDIC/NCUA insurance limits, and state-specific tax treatment aren’t factored in — check your bank’s disclosure documents for those details.
Step-by-step sample calculations
Two scenarios show how deposit size, term, and compounding frequency change the final balance.
$10,000 at 4.5% APY for 12 months
I’m putting $10,000 into a 1-year CD with a 4.5% APY, compounded monthly. What will it be worth at maturity?
Given inputs
- Deposit: $10,000
- APY: 4.5%
- Term: 12 months
- Compounding: Monthly (n=12)
Result
- Formula: 10,000 × (1 + 0.045÷12)^(12×1)
- Total balance: ≈ $10,459.35
- Interest earned: ≈ $459.35
$25,000 at 3.8% APY for 5 years
I’m locking $25,000 into a 5-year CD at 3.8% APY with daily compounding. How much interest will that earn overall?
Given inputs
- Deposit: $25,000
- APY: 3.8%
- Term: 5 years
- Compounding: Daily (n=365)
Result
- Formula: 25,000 × (1 + 0.038÷365)^(365×5)
- Total balance: ≈ $30,203.11
- Interest earned: ≈ $5,203.11 — a longer term and more frequent compounding both contribute to the larger total gain here.
CD Calculator Mistakes to Avoid
Confusing APY with a simple interest rate
Since APY already reflects the effect of compounding over a full year, applying the compounding formula to an APY as if it were a simple annual rate will slightly overstate your final balance.
Comparing CDs by rate alone, ignoring term
A higher APY on a shorter term doesn’t necessarily out-earn a lower APY on a longer term. Because of that, it’s worth comparing the actual dollar amount at maturity, not just the two percentages side by side.
Forgetting that CD interest is taxed annually
Even though you can’t access the money until maturity, interest credited each year on a CD is generally taxable in that year. As a result, a multi-year CD can generate a tax bill before you ever touch the funds.
Ignoring early withdrawal penalties
This calculator assumes the CD is held for its full term. However, most banks charge a penalty — often several months of interest — if you withdraw before maturity, which this estimate doesn’t subtract.