This CD rates calculator turns a certificate of deposit's disclosure into money: what the certificate is worth at maturity, how much interest is left after the tax rates you enter, how the interest builds twelve months at a time on a term over a year, and roughly what you would receive if you closed it early.
It works from the annual percentage yield (APY), which every bank must state and which already contains the compounding, so there is no box for how often interest compounds. The starting values are illustrative: the $10,000 deposit, 4.00% APY, 22% federal tax rate and 90-day penalty are round numbers chosen to show the arithmetic, not any institution's rate. Replace them with the figures from your disclosure; the last section says where real rates are published.
CD calculator
Enter the APY from the certificate’s disclosure, not a headline rate from an advert. The starting values below are illustrative.
Works from the APY, which by law already includes compounding and assumes the interest stays in the certificate until it matures. If the interest is paid out instead, tick the box: the calculator then uses simple interest at the APY, which for such certificates longer than a year Regulation DD allows to be disclosed as equal to the rate; the penalty is then taken at that rate too. Otherwise the penalty is modelled as days of simple interest at the rate that compounds daily to the APY; your certificate’s own schedule decides the real figure. Taxes use the rates you enter and ignore deductions. Educational estimate, not financial or tax advice.
Why it asks for the APY, not the interest rate
Regulation DD, the Truth in Savings rule, requires a certificate's disclosure to give both figures, "using those terms". The interest rate is the annual rate "which does not reflect compounding"; the APY reflects "the total amount of interest paid on an account, based on the interest rate and the frequency of compounding for a 365-day period". So APYs compare cleanly across certificates that compound differently, as APR vs APY explains.
The regulation's Appendix A gives the formula, APY = 100 × [(1 + Interest ÷ Principal)^(365 ÷ Days in term) − 1], and has the bank "assume that all principal and interest remain on deposit for the entire term". Turned round, the interest over t years is the deposit × [(1 + APY)^t − 1]: the calculator's maturity arithmetic unless you tick its payout box. Asking for the compounding frequency too would count it twice. The same appendix drops the remain-on-deposit assumption where the account requires you to withdraw interest during the term: the interest and the APY then "shall reflect that requirement", which is what the payout box models.
One simplification: the calculator counts a month as a twelfth of a year, while the regulation uses actual days. On an illustrative $10,000 at 4.00% APY, half a year gives $198.04 of interest and 182 days $197.49; the bank's day count governs.
What each input does
Deposit ($). Assumed to stay untouched until maturity, as the APY itself assumes.
APY (%). From the certificate's disclosure, not an advert or a comparison table. The 4.00% default is illustrative. Anything above 20 is treated as 20; as with every capped input below, the result opens with a line saying so.
Term (months). Whole months, from 1 to 120; a fraction is rounded to the nearest month, and a figure outside that range is treated as the nearer end.
Interest is paid out to me, not added to the certificate. A tick box, off by default. Ticked, the calculator stops compounding and uses simple interest at the APY; the section on what the calculator does not do says which certificates that fits.
Federal marginal rate (%). The IRS lists interest on certificates of deposit among its examples of taxable interest. The calculator applies the single rate you type, with no brackets, and treats more than 50 as 50; the 22% default is illustrative, not a guess at yours.
State and local rate (%). Added to the federal rate and applied with it; more than 20 is treated as 20. The default is zero; the calculator knows no state's rules and ignores deductions.
Penalty (days of interest). From the certificate's schedule; three months' interest is roughly 90 days, and more than 730 is treated as 730. Regulation D's floor, seven days' simple interest, covers only money withdrawn within six days of a deposit or a partial withdrawal; above it, the schedule is the bank's choice. The 90-day default is illustrative.
Withdraw after month. 0 holds to maturity. An earlier month adds an exit estimate; a month at or after maturity, a line saying no penalty applies.
Reading the result
Maturity value, interest and tax
The large figure is the value at maturity, assuming the interest stays in the CD until it matures; with the payout box ticked it reads "in total, deposit plus interest paid out" instead. Below come interest before tax, tax at your combined rate (22.0% on the illustrative defaults), interest after tax, and an after-tax APY: the APY × (1 − your combined rate), labelled that way in the result. It is the same for every term, 3.12% on the illustrative 4.00% and 22%, so it does not drift with the length of the certificate the way the after-tax interest turned into an annual rate would. HYSA vs CD vs T-bills sets that kind of after-tax figure against a savings account and a Treasury bill.
The twelve-month rows
A term over twelve months adds a table in twelve-month blocks, labelled by month: "1–12", "13–24" and so on, with a shorter last block on a term that is not a whole number of years ("13–18" on an 18-month term). Each row gives the balance at the end of the block and the "Interest in these months"; with the payout box ticked, the middle column shows the deposit instead, since the interest has left the certificate. A note under the table says each row is twelve months from the day the certificate opens, so the rows line up with tax years only if it opens in January, and exactly only if it opens on the first.
The rows reflect tax timing. IRS Publication 550 says: "If you buy a CD with a maturity of more than 1 year, you must include in income each year a part of the total interest due and report it in the same manner as other OID", original issue discount being generally included "as it accrues". So the tax line above is the whole term's total, not one year's bill. Interest paid at fixed intervals of a year or less, and interest on a certificate of a year or less paid in one sum at maturity, generally count when you receive it or are entitled to it without paying a substantial penalty.
The early-withdrawal estimate
With a withdrawal month set, the calculator shows the interest earned by then (the deposit's growth at the APY to that month, or simple interest at the APY with the payout box ticked), the penalty, and what you would receive: deposit plus interest, less penalty. With the box ticked, the line says the total includes interest already paid to you along the way. The penalty is your number of days of simple interest on the whole deposit, at the interest rate that compounds daily to the APY: about 3.92% for an illustrative 4.00% APY. With the box ticked it is taken at the APY itself, since the box treats the APY as the rate. Regulation DD requires the disclosure to state "how it is calculated, and the conditions for its assessment", so your certificate's terms hold the real formula; this is a model of the days-of-interest kind.
If the penalty exceeds the interest earned, a warning gives the amount that would come out of your deposit "at a bank whose terms allow the penalty to reach principal". Whether yours does is a line in the schedule; the penalty page shows the shapes schedules take. The estimate is before tax: Publication 550 has you report the full interest "without subtracting the penalty" and deduct the penalty on Schedule 1 (Form 1040), which the calculator does not do.
A worked example on the default inputs (illustrative)
Press Calculate without changing anything (a $10,000 deposit, an illustrative 4.00% APY, 12 months, an illustrative 22% federal rate, no state rate) and it shows:
| Line | Shown |
|---|---|
| At maturity | $10,400.00 |
| Interest before tax | $400.00 |
| Tax at the rates you entered (22.0%) | $88.00 |
| Interest after tax | $312.00 |
| After-tax APY (APY × (1 − tax rate)) | 3.12% |
For a 365-day term Appendix A's formula reduces to APY = 100 × (Interest ÷ Principal), so the interest is exactly 4.00% of the deposit and the tax 22% of $400. The after-tax APY is 4.00% × (1 − 0.22). A 12-month term shows no table of twelve-month rows, and a withdrawal month of 0 no exit line.
Change only the term to 24 months and the result is $10,816.00, with a "1–12" row of $10,400.00 and $400.00 of interest and a "13–24" row of $10,816.00 and $416.00, the extra $16 being interest on interest. Tax at the illustrative 22% is $179.52, leaving $636.48, and the after-tax APY still reads 3.12%, as it does at every term.
Tick the payout box as well and the headline becomes "$10,800.00 in total, deposit plus interest paid out": $400.00 of simple interest in each twelve-month row, $800.00 in all, with the $10,000.00 deposit in the middle column. Tax at the illustrative 22% is $176.00, and the after-tax APY is again 3.12%.
Leaving early (illustrative)
The one-year default with the illustrative 90-day penalty and a withdrawal month:
| Withdraw after | Interest earned | Penalty | You would receive about |
|---|---|---|---|
| Month 2 | $65.58 | $96.71 | $9,968.87 |
| Month 3 | $98.53 | $96.71 | $10,001.82 |
| Month 6 | $198.04 | $96.71 | $10,101.33 |
At month 2 the calculator warns that $31.13 would come out of the deposit. By month 3 the interest has just overtaken the penalty, leaving $1.82 for three months' use of $10,000.
The penalty page prints $98.63 for the same 90 days because it treats an illustrative 4.00% as the interest rate; the calculator treats it as the APY and backs out the slightly lower rate behind it.
What the calculator does not do
No bank's rate or penalty. You supply both, from the same disclosure.
Only one model of paid-out interest. The payout box pays simple interest at the APY. That fits a certificate whose APY equals its rate. Under Appendix A, one of more than a year that does not compound and requires you to withdraw interest at least annually "may be disclosed as equal to the interest rate", and the regulation then requires its disclosure to state "that interest cannot remain on deposit and that payout of interest is mandatory". It fits less well a certificate that compounds but lets you take the interest, which must say its APY "assumes interest remains on deposit until maturity and that a withdrawal will reduce earnings": if it compounds more often than yearly, its rate is below its APY, so the box overstates. On an illustrative $10,000 at 4.00% APY compounding daily, two years of interest credited and taken out monthly comes to about $785.70, not the $800.00 the box shows. With the box ticked the penalty is taken at the APY, matching a certificate whose APY equals its rate: $98.63 for the illustrative 90 days, against $96.71 unticked.
Not for a brokered CD's exit. An SEC staff investor bulletin says a brokered CD generally pays simple rather than compound interest and generally has no early-withdrawal penalty; it can generally be sold on a secondary market instead, "subject to market conditions". The exit estimate models a bank's penalty, not a sale. Brokered CD vs bank CD prices that sale against a bank penalty.
No compounding frequency, by design. The APY already embeds it; the payout box only switches compounding off, and daily compounding appears only in backing out a rate for the penalty.
No tax rules beyond your rates. Inside an IRA the wrapper decides when interest is taxed, and the IRS tells payers not to report interest "earned but not distributed from an IRA"; what an IRA CD is covers the wrapper.
Nothing after maturity, and no partial exit. The disclosure must state "whether or not the account will renew automatically at maturity"; a renewal's rate is one the calculator cannot know. The exit estimate closes the whole certificate.
Where to find real CD rates
Take the APY from the institution: the certificate's disclosure or its own rate page, for your term and balance. Which banks have the best CD rates explains why rate tables disagree, where the FDIC publishes dated national averages by term, and how to check an offer at the institution.
If the date you need the money is uncertain, run the exit estimate at several months. Two structures change that line: a CD ladder staggers maturities, and a no-penalty CD gives up some rate to drop the penalty.
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