CD Calculator

What Is a CD (Certificate of Deposit)?

Two things separate a CD from a savings account: the rate cannot move while the term runs, and neither can the money. Everything else about the product follows from that pair.

The Trade You Are Actually Making

You hand a bank a lump sum and agree not to touch it for an agreed number of months. In return the bank fixes the yield for the whole term, which it can afford to do because it now knows precisely how long it has the money. A savings account is the opposite bargain — you withdraw whenever you like, and the bank reprices whenever it likes.

So the choice between them is never only a rate comparison. A locked yield is an advantage when rates fall and a liability when they rise, and the term length is where you place that bet. The way to size it is mechanical: run the same deposit at several terms and read what the extra commitment is actually paying you.

Before you can run any offer through this page, the bank has to have told you four things. The Truth in Savings Act (Regulation DD, § 1030.4) requires a time-account disclosure to state the annual percentage yield, the maturity date, that a penalty will or may be imposed for early withdrawal and how it is calculated, and whether the account renews automatically. An advertisement missing any of those is not yet an offer you can price.

APY Is the Only Rate You Need

Banks quote CDs in annual percentage yield, and federal rules define that term precisely rather than leaving it to marketing. Appendix A to Regulation DD sets the calculation as 100 × [(1 + interest ÷ principal) raised to (365 ÷ days in term), minus 1] — the yield a deposit genuinely delivers over a year, with compounding already folded in.

The practical consequence is that you never have to ask how often a bank compounds. Daily, monthly, quarterly, at maturity: whichever it is, the advertised APY has already absorbed it, so two offers quoted in APY are directly comparable even when their compounding schedules differ. A plain "interest rate" quoted without the word yield has not absorbed it, and will always print smaller than the APY of the same account.

The regulation supplies its own worked example: $1,000 that earns $61.68 over 365 days carries an APY of 6.17%. Type $1,000, 6.17 and 12 months into the fields above and the tool returns 61.70 interest earned. The two-cent gap is the regulation rounding its published yield to two decimals, and it is the cleanest available proof that this calculator inverts the federal definition rather than approximating it.

The CD Variants You Will See Advertised

The calculator models one rate applied to one term. That covers the product most banks lead with, and it covers the others only partly:

• Standard term CD — one deposit, one fixed rate, one maturity date. This is exactly what the four fields describe.
• No-penalty or liquid CD — withdrawable after an opening window with nothing forfeited, in exchange for a lower yield. Price it by entering the lower APY and comparing the two maturity values.
• Bump-up CD — you get one option to move to the bank's current rate if rates rise. The tool cannot model the switch; run the starting rate and the hoped-for rate as separate scenarios.
• Step-up CD — the rate changes on a published schedule. The advertised APY is the blended yield across the full term, so entering that figure with the full term still gives the right maturity value.
• Callable CD — the bank may end the deal early, which it will want to do after rates fall. The headline yield is higher because you are the only side that cannot cancel.
• Brokered CD — bought through a brokerage and tradable on a secondary market. Held to maturity it behaves like a standard CD; sold early its price is whatever a buyer offers, which can be below what you paid.

For the machinery underneath a quoted yield — compounding frequency, and what changes once you keep adding money — work the same deposit through our Compound Interest Calculator.

How Do You Calculate CD Interest?

One exponent and one subtraction. Because the advertised APY already contains the compounding, the calculation needs no compounding frequency, no rate conversion and no day-count convention — it needs the term expressed as a fraction of a year.

The CD Formula, Written Out

Two lines, and the first is the APY definition turned inside out:

Maturity = deposit × (1 + APY) ^ years

Interest = Maturity − deposit

deposit = the lump sum going in, in dollars
APY     = advertised yield as a decimal      (4.50%  →  0.045)
years   = the term as a fraction of a year   (18 months → 1.5)

Set that beside Appendix A's definition of APY and the two are one equation solved for different unknowns. The regulation starts from a known dollar figure and derives the yield; this page starts from the published yield and derives the dollars. Nothing is lost in the round trip, which is why the maturity value is exact rather than an estimate — assuming the bank quoted honestly and you hold to the end.

When Years is selected, the term is converted before anything is raised to a power:

years = term          (Years selected)
years = term ÷ 12     (Months selected)

36 months and 3 years therefore return the identical figure: $10,000 at 4.50% APY earns 1411.66 whichever unit you pick. Notice too what the equation does not contain. No compounding frequency, because the APY absorbed it. No monthly contribution, because a CD takes one lump sum. No fee, because a standard CD does not carry a maintenance charge. The entire product is three numbers and an exponent.

Step by Step

A full run worked by hand — $25,000 at 4.50% APY for 18 months:

• Convert the APY to a decimal: 4.50 ÷ 100 = 0.045.
• Convert the term to years: 18 ÷ 12 = 1.5.
• Add one to the decimal rate to get the growth base: 1 + 0.045 = 1.045.
• Raise that base to the term: 1.045 to the power 1.5 = 1.06825377.
• Multiply by the deposit: 25,000 × 1.06825377 = 26,706.34. That is the maturity value.
• Subtract the deposit to isolate the interest: 26,706.34 − 25,000 = 1,706.34.

One check catches most arithmetic slips. The compounded answer must always come out above simple interest at the same rate, and never far above it on a short term: 25,000 × 0.045 × 1.5 is 1,687.50, against the calculator's 1,706.34. The 18.84 between them is the compounding, and it is the only thing the exponent adds.

Worked Example: $25,000 at 4.50% APY for 18 Months

Typed in as 25000, 4.5, Months, 18, the tool returns 1706.34 interest earned as the headline, with Maturity Value 26706.34 and Term 18 months at 4.50% APY beneath it. Switch the unit to Years and enter 1.5 and every figure is identical, because the conversion happens before the exponent rather than after.

Result on those inputs

1706.34 interest earned · Maturity Value 26706.34 · Term 18 months at 4.50% APY

That $1,706.34 is gross. It is the number the bank credits, not the number you keep: the interest is taxable in the year it is credited, and the figure evaporates if the CD is broken before month 18. Both of those are handled further down, and neither changes the arithmetic above.

Why Six Months Does Not Pay Half a Year

The most common surprise on this page: a 6-month CD at 5.00% APY on $10,000 pays 246.95, not 250. Half a year's yield is not half a year's compounding. The correct half-term growth factor is the square root of 1.05, which is 1.0246951 — slightly below the 1.025 that halving the rate would give you, because the yield you were quoted assumed a full year of interest earning interest.

The same effect runs the other way over long terms, and it is much larger. $10,000 at 4.50% for five years earns 2461.82, while five separate one-year CDs at that rate would earn 5 × 450.00 = 2250.00. The extra 211.82 is interest that the earlier years' interest went on to earn — the reason a long quote is worth more than its annual rate makes it sound.

Using This CD Calculator Online

Four fields, no sign-in, and no rate table pulled from anywhere. Everything the tool knows arrives from what you type, which is deliberate — an embedded rate would be wrong the week after it was written.

What Each Field Wants

• Deposit Amount ($) — the lump sum going in. It must be above zero; a blank or zero deposit produces the "Check your inputs" notice rather than a row of zeros.
• APY (Annual Percentage Yield) (%) — the advertised figure as a percentage, not a decimal: type 4.5, not 0.045. A negative entry is rejected. Zero is accepted and is a legitimate answer — it returns 0.00 interest with the maturity value equal to the deposit.
• Term Unit — a two-way switch between Months and Years, sitting on Months when the page loads.
• Term Length — how many of that unit, and decimals are allowed. 1.5 Years and 18 Months describe the same CD and return the same numbers.

There is no separate compounding-frequency field, and its absence is the point rather than an omission. A quoted APY has already accounted for the schedule, so asking for it again would let you double-count the same compounding.

What the Page Will Not Do For You

The fields open empty and the result panel stays blank until all four are filled and submitted — there is no pre-loaded example sitting in the boxes. If a figure is missing, or zero or negative where it cannot be, the panel switches to a "Check your inputs" notice instead of printing a wrong number, which is the behavior you want from a tool people use to compare real offers.

There is no currency selector and no rate lookup. The dollar sign beside the deposit field is a label, not a conversion — the arithmetic is unit-agnostic, so a deposit in pounds against a yield quoted the same way returns a correct answer in pounds. What no calculator can tell you is whether the APY you typed is a good one; that judgment needs several banks' offers, and it is the reason to run this page more than once.

Weighing the locked term against money you can reach at any time? Price the flexible side of that decision with the Savings Calculator.

How to Read Your Result

The output is three lines and only the first is a headline. Reading the other two is how you catch a mistyped term before you act on the number.

The Three Lines

Figures print as plain numbers, without thousands separators or a currency symbol, so a maturity value of 10450.00 is ten thousand four hundred fifty dollars rather than one hundred four thousand. The Term line is the quickest typo detector here: enter 5 with the unit left on Months and it reads 5 months, which is how you discover you meant 5 years before you compare it against anything.

Turning the Headline Back Into a Yearly Number

The headline is term interest, and term interest equals annual interest only at exactly 12 months. A five-year run at 4.50% on $10,000 returns 2461.82, which is 24.62% of the deposit — a total, not a rate. Divided across the term it is 492.36 a year, and that sits above the 4.50% headline for the same reason as always: the later years are earning on the earlier years' interest.

For ranking offers of unequal length, the APY is already the annualized figure, so compare rate against rate and let the dollars follow. Maturity values only rank cleanly when the terms match. A 4.50% 18-month CD and a 4.75% 12-month CD cannot be ordered by their maturity values at all, because they release the money on different dates and what you do with it in the gap is part of the answer.

What You Actually Keep

CD interest is ordinary taxable income in the year it is credited. The IRS lists certificates of deposit explicitly among the accounts that generate taxable interest, and the bank issues a Form 1099-INT once you have earned $10 or more for the year — including on a multi-year CD whose money you have not touched and cannot reach.

That converts the headline into an after-tax figure in one multiplication. The 450.00 that $10,000 earns at 4.50% over a year becomes 351.00 in a 22% federal bracket, an effective 3.51%, or 306.00 at 32%, an effective 3.06%. State income tax, where it applies, comes off after that. A CD held inside an IRA defers the whole charge the way the account defers everything else.

The other subtraction worth making is inflation, because a locked yield only builds purchasing power when it outruns rising prices — size that gap with the Inflation Calculator.

CD Interest Chart: What $10,000 Earns

Every cell below is this calculator's own output for a $10,000 deposit, stated as interest earned across the full term. Interest scales exactly with the deposit, so $50,000 is five times the cell and $2,500 is a quarter of it.

Three patterns are worth carrying away from the grid. Every one-year cell is the APY times the deposit exactly, which is what the yield definition promises. Every five-year cell beats five times its own one-year cell — by $166.53 at 4.00% and by $211.82 at 4.50%. And half a point of APY is worth $50.00 on a one-year CD but roughly $300 on a five-year one, which is why rate shopping repays the most effort on the terms people are least inclined to shop.

The Same Rate Across Deposit Sizes

One year at 4.25% APY, from a starter balance up to the federal insurance limit:

The last row lands on the FDIC's standard coverage limit, and it is where arithmetic stops being the whole story. Deposit insurance is calculated principal plus accrued interest through the date of a bank's failure, so a $250,000 deposit is fully covered on day one and the $260,625.00 it becomes is not. Balances that will cross the line before maturity are usually opened below it, or split across banks or ownership categories.

CD Examples: Four Runs Through the Calculator

Four situations that come up constantly, each entered exactly as written and reported exactly as returned.

Rows one and two say something the individual figures do not. The six-month CD carries the higher rate — 5.00% against 4.25% — and still returns 58% of the twelve-month dollars, because it is invested for half the time. Rate is what people shop for; term is what decides the size of the check.

Row four is the compounding row. $50,000 at an unremarkable 4.00% becomes $60,832.65 over five years. Simple interest at the same rate would have paid $10,000 flat, so $832.65 of that total is interest the interest earned — nearly 8% of the return, produced by nothing except leaving it alone.

Early Withdrawal Penalties and CD Ladders

Everything above assumes the CD reaches maturity. The moment it does not, a second calculation applies that this tool does not perform — and it is the one that can turn the safest product in retail banking into a loss.

What Breaking a CD Costs

Banks state the forfeiture as a number of months of interest, and the schedule is theirs alone — there is no legally fixed rate. Regulation DD requires the disclosure to say that a penalty will or may be imposed and exactly how it is calculated, which makes the account disclosure the only place the real figure for your CD lives. Typical schedules run around three months of interest on terms under a year and six to twelve months on longer ones.

The number that catches people is what happens early in a long CD. Take $10,000 in a five-year CD at 4.50% with a six-month interest penalty: six months of simple interest at the CD's own rate is $225. Break it at the twelve-month mark and the calculator says 450.00 has accrued, so you keep $225 of it. Break it at three months, when only 110.65 has accrued, and the penalty is larger than the interest — you receive $9,885.65, and $114.35 of your own principal has gone.

That is the entire case for matching the term to the money. The penalty is not a cut of the profit; it is a charge measured in interest the CD would have paid, and it does not stop once the interest runs out.

Laddering, With the Cost Shown

A ladder splits one deposit across staggered terms so something matures every year. Put $25,000 into five $5,000 rungs at 4.50%, one year through five, and the rungs return 225.00, 460.12, 705.83, 962.59 and 1230.91 — $3,584.45 of interest in total across the five maturity dates.

The same $25,000 in a single five-year CD at that rate earns $6,154.55. On this comparison the ladder costs $2,570.10, and that is the price of a rung coming due every year instead of waiting five. A ladder run properly narrows the gap by rolling each matured rung into a fresh five-year CD, so that after four years you hold five-year rates with annual access. The gap never closes completely, and what it buys is the ability to never need the penalty above.

Money you are confident you will not need for a decade is a different question entirely, and belongs in a different model — try the Investment Calculator.

Both structures price out with the same four fields. Run each rung as its own calculation, add the interest figures, and set the total against a single run at the longest term you could genuinely commit to — the difference between those two numbers is what your liquidity is costing you, stated in dollars rather than in feelings.

Limits: When This Calculation Does Not Apply

The arithmetic is exact. The situations it describes are narrower than the shelf of products called CDs, and these are the gaps.

• Terms are measured in whole twelfths of a year, not in days. Six months is treated as exactly half a year — 182.5 days — while a real 6-month CD runs 181 to 184 days depending on when it starts. On $10,000 at 5.00% that is a range of $244.90 to $249.01 against this page's $246.95, so expect a bank's own figure to differ by a few dollars per $10,000.
• Leap days are not counted. A five-year term usually contains 1,826 days rather than 1,825; at 4.50% on $10,000 the day-exact figure is $2,463.32 against the calculator's $2,461.82, a difference of $1.50.
• Nothing is paid out along the way. If you take the interest as monthly income instead of letting it sit, you receive something closer to simple interest and end up below these totals — an APY assumes interest stays in the account until maturity, and Regulation DD requires the bank to disclose that assumption.
• No penalty, no tax and no inflation is deducted. Every figure is gross interest at maturity, before the 1099-INT and before any early-withdrawal forfeiture.
• No rate is looked up. Nothing on this page knows what any bank is paying today; every number in every table came from a rate typed into the field, and those rates are illustrations rather than offers.
• Bump-up exercises, step-up schedules, add-on deposits and callable redemptions are not modeled. Each of them changes the rate or the balance mid-term, and the tool applies one rate to one balance for the whole term.
• Brokered CDs sold before maturity sit outside this completely. Their resale price is set by a secondary market that reprices with interest rates, so a sale can return less than the deposit even though the CD itself never missed a payment.

What is not a limitation is the credit risk. A CD at an FDIC-member bank is insured to at least $250,000 per depositor, per insured bank, per ownership category, principal and accrued interest together, and the SEC's investor education material is blunt that the limit covers all accounts in your name at that bank rather than each CD separately. Inside that ceiling and held to the maturity date, the value this page prints is about as close to a guaranteed number as personal finance ever gets.