CD Calculator
A certificate of deposit, or CD, is one of the most predictable places to park money you won't need for a fixed period — you lock in a rate, commit to a term, and know almost exactly what you'll have at the end. That predictability is the whole appeal, but it also means the math is worth checking before you commit, since early withdrawal penalties can eat into returns if your timeline is wrong. This CD calculator takes your deposit amount, annual percentage yield (APY), term length, and compounding frequency, and tells you exactly what your CD will be worth at maturity, along with the total interest you'll earn along the way. Whether you're comparing a 6-month CD at one bank against a 12-month CD at another, or deciding whether a CD ladder makes sense for an upcoming expense, having the exact maturity number in front of you — rather than a rough mental estimate — makes the comparison much easier.
How the CD formula works
CD interest compounds the same way a savings account does, using the standard compound interest formula, applied over the CD's fixed term:
Maturity value = Deposit × (1 + APY/n)^(n×t) Total interest = Maturity value − Deposit
Where APY is the annual percentage yield as a decimal, n is the number of compounding periods per year (most CDs compound daily or monthly), and t is the term length in years. Because APY already reflects the effect of compounding — unlike a simple stated interest rate — using it directly in this formula, along with the bank's actual compounding frequency, gives an accurate maturity figure that matches what your statement will show.
Step-by-step calculation
- Convert the CD's term length into years, since the formula works in fractional years (a 9-month CD is 0.75 years).
- Convert the compounding frequency into a number of periods per year — daily is 365, monthly is 12, quarterly is 4.
- Divide the APY by the number of compounding periods to get the rate per period.
- Raise (1 + rate per period) to the power of total periods (frequency × term in years).
- Multiply by your deposit amount to get the maturity value, then subtract the original deposit to isolate total interest earned.
Worked example
A $10,000 deposit into a 12-month CD at 4.75% APY, compounded daily: Maturity value = 10,000 × (1 + 0.0475/365)^(365×1) ≈ $10,486.25. Total interest earned over the year is about $486.25 — a fixed, guaranteed return as long as the CD is held to maturity.
How CDs compare to savings accounts and why the term length matters
The core tradeoff with a CD is liquidity for yield: banks typically pay a higher rate on a CD than on a standard savings account precisely because you're agreeing not to touch the money until maturity. Break that agreement early, and most CDs charge an early withdrawal penalty — often calculated as a certain number of months' worth of interest, which can eat into or even exceed the interest you've earned if you withdraw shortly after opening the account. That's why term length isn't just a detail to plug into a formula; it's a real commitment that should match money you're confident you won't need before the maturity date.
Term length also interacts with interest rate environments in a way that's worth thinking through before locking in. When rates are expected to rise, shorter-term CDs (3 to 6 months) let you reinvest sooner at a potentially higher rate, while a longer-term CD locks you into today's rate even if better offers appear later. When rates are expected to fall, the opposite logic applies — locking in a longer term captures today's higher rate before it disappears. A CD ladder, where you split money across several CDs with staggered maturity dates (say, 3-month, 6-month, 9-month, and 12-month CDs opened simultaneously), is a common strategy to get some of both: regular access to a portion of your funds as each CD matures, while still benefiting from typically higher longer-term rates on the rest.
Another detail worth checking directly with your bank: whether the CD compounds daily, monthly, or some other frequency, since this calculator lets you match that exactly rather than assuming a default. More frequent compounding modestly increases your effective return for the same stated APY, which is why APY (which already accounts for compounding) is the number to compare across banks rather than a raw interest rate, which can understate what you'll actually earn.
Frequently asked questions
What happens if I withdraw money from a CD before it matures?
Most banks charge an early withdrawal penalty, commonly calculated as a set number of months of interest (for example, 90 days of interest on a 1-year CD). In some cases, especially with early withdrawals shortly after opening, the penalty can exceed the interest earned so far, effectively costing you a small amount of your original principal.
Is CD interest taxable?
Yes — in the US, interest earned on a CD is generally taxable as ordinary income in the year it's earned (or credited), even if you don't withdraw it, unless the CD is held inside a tax-advantaged account like an IRA.
What's the difference between APY and APR on a CD?
APY (annual percentage yield) already factors in compounding, showing your actual annual return. APR (annual percentage rate) is the simple stated rate without compounding factored in. Since virtually all CDs are advertised using APY, that's the number this calculator expects.
Are CDs FDIC insured?
CDs from FDIC-member banks are insured up to $250,000 per depositor, per bank, per ownership category — making them one of the lowest-risk places to hold money for a fixed term, which is part of why they typically pay less than riskier investments.
Is a CD better than a high-yield savings account?
It depends on your timeline and the current rate environment. A CD often pays a higher fixed rate but locks up your money and penalizes early withdrawal, while a high-yield savings account offers full liquidity but a variable rate that can drop at any time. If you have a specific date you'll need the funds and want rate certainty until then, a CD is usually the better fit.
Can I add more money to a CD after opening it?
Standard CDs don't allow additional deposits after the initial funding — you'd need to open a new CD for additional funds. Some banks offer 'add-on' CDs specifically designed to allow extra deposits during the term, but these are a distinct product, not the default.