ReckonBoxHow the CD calculator works
A certificate of deposit is a deposit account that pays a fixed rate for a fixed term, with a penalty for taking the money out before the term ends. Enter the deposit, the rate, the term in months and your tax rate, and this returns the maturity value, the yield, and what an early exit would actually cost.
The last part is why this page exists. Every CD calculator on the first page of results works out the maturity value. None of them prices the penalty.
The formula, which nobody publishes
Balance = P x (1 + r/n)^(n x t)
P is the deposit, r the nominal rate, n the compounding periods per year and t the term in years. A $10,000 deposit at 4.5% compounded monthly for one year matures at $10,459.40.
calculator.net, which ranks second for the term, publishes no formula at all. The bank calculators do not either, which is unsurprising: they exist to make a rate look attractive rather than to teach the arithmetic behind it.
The rate and the APY are different numbers
APY is the yield once compounding is counted, so it is always at least the nominal rate the bank quotes. At 4.5% compounded monthly, the APY is 4.594%.
Compounding frequency is the only reason two CDs advertising the same rate can pay different amounts:
| Compounding | Interest on $10,000 for one year | APY |
|---|---|---|
| Annually | $450.00 | 4.500% |
| Semiannually | $455.06 | 4.551% |
| Quarterly | $457.65 | 4.577% |
| Monthly | $459.40 | 4.594% |
| Daily | $460.25 | 4.603% |
Ten dollars and twenty-five cents separates the two ends. Worth knowing about, and smaller than the marketing around it suggests.
What breaking a CD early costs
Penalties are quoted as a number of days of interest, and the bank sets the number. Per the OCC's consumer guidance, CD penalties sit under 12 CFR 1030, the Truth in Savings Act (Regulation DD), which sets a floor and no ceiling: pull the money within the first six days after deposit and the penalty is at least seven days of simple interest. Above that floor it is a contract term, which is why Bankrate and NerdWallet report common schedules running from around 90 days of interest on a one year CD up to 365 days on a five year one.
The penalty is charged on the principal at the nominal rate, so it does not shrink just because you have earned less than it:
Penalty = P x r x (days / 365)
On our $10,000 CD, a 90 day penalty is $110.96 whether you break it in month one or month eleven.
The case no ranked calculator can show you
Break that CD after one month and you have earned $37.50 of interest. The penalty is $110.96. You get back $9,926.54, which is $73.46 less than you deposited.
Regulation DD permits exactly this: a penalty may reach into principal when the interest earned does not cover it. So a CD is not a product where the worst case is earning nothing. The worst case is losing money, and it arrives quietly in the first months of the term.
| Withdraw after | Interest earned | Penalty | You receive |
|---|---|---|---|
| 1 month | $37.50 | $110.96 | $9,926.54 |
| 6 months | $227.12 | $110.96 | $10,116.16 |
| 12 months (maturity) | $459.40 | none | $10,459.40 |
Tax takes a share every year
CD interest is taxed as ordinary income in the year it is credited, which on a multi-year CD means paying tax on money you cannot access yet.
At a 22% marginal rate, the $459.40 above leaves $358.33. That turns a 4.594% APY into an effective 3.583%, which is the figure to hold against any tax-free alternative. calculator.net is the one ranked calculator that takes a tax rate at all, and it deserves credit for that.
Tax treatment varies by country and account type, so a CPA or tax adviser is the right check on your own position.
What this calculator does not do
It won't tell you whether a CD is a sensible place for your money, or which term to pick. Those depend on when you need the cash and what else is available to you.
Specific banks' penalty schedules are out of scope. They change, they vary by product within the same bank, and a table of them here would be wrong within months. The penalty field takes the number from your own account agreement, which is where the binding version lives.
Nor does it model laddering, automatic renewal at the prevailing rate, or callable CDs. Results are arithmetic on your inputs, not financial advice. For decisions about your money, speak to a licensed financial adviser. To compare the yield against a different compounding frequency, the APY calculator does that directly, and the compound interest calculator handles a balance you keep adding to.
Frequently asked questions
How is CD interest calculated? A CD compounds at a fixed rate for a fixed term, so the balance is the deposit times (1 + r/n) raised to the power n times t, where r is the nominal rate, n the compounding periods per year and t the years. A $10,000 deposit at 4.5% compounded monthly for one year matures at $10,459.40.
What is the difference between a CD interest rate and its APY? The interest rate is the nominal figure and the APY is what it becomes once compounding is counted, so the APY is always the higher of the two unless interest compounds only once a year. At 4.5% compounded monthly the APY is 4.594 percent. Banks advertise the APY because it is larger, which is fair since it is also the number that lets you compare two offers properly.
What is the penalty for withdrawing from a CD early? Penalties are charged as a number of days of interest and the bank sets the amount. Per the OCC, CD penalties fall under 12 CFR 1030, the Truth in Savings Act (Regulation DD), which sets a minimum and no maximum: withdraw within the first six days after deposit and the penalty is at least seven days simple interest. Bankrate and NerdWallet report common schedules running from around 90 days of interest on a one year CD to 365 days on a five year one.
Can an early withdrawal penalty take money from the principal? Yes, and this is the part most calculators cannot show you because they have no penalty field at all. Regulation DD permits the penalty to reach into principal when the interest earned does not cover it. Break a $10,000 CD paying 4.5 percent after one month with a 90 day penalty and you get back $9,926.54, which is $73.46 less than you deposited.
How much tax do you pay on CD interest? CD interest is taxed as ordinary income at your marginal rate in the year it is credited, even on a multi-year CD where you cannot access the money yet. At a 22 percent marginal rate, $459.40 of interest leaves $358.33, which turns a 4.594 percent APY into an effective 3.583 percent. Tax treatment varies by country and by account type, so a CPA or tax adviser is the right check on your own position.
Does compounding frequency change what a CD pays? Yes, though less than people expect at these rates. On $10,000 at 4.5 percent for a year, annual compounding pays $450 and daily compounding pays $460.25. The frequency matters more the higher the rate and the longer the term, and it is the only reason two CDs quoting the same rate can pay different amounts.
What happens when a CD matures? The deposit and its interest become available, usually inside a short grace period, after which many banks automatically renew the CD at whatever rate then applies. That renewal rate is not the rate you originally locked, which is the mechanism behind a lot of unintentionally rolled-over money.
Is a CD calculator the same as a compound interest calculator? The core arithmetic is identical, and this page exists for the two things around it. CD terms are quoted in months, so an 18 month term needs a months field rather than years. And the early withdrawal penalty is specific to CDs and is the thing that most changes the answer when the money is needed sooner than planned.