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CD Interest Calculator

A certificate of deposit pays a fixed, bank-guaranteed yield in exchange for locking your money up for a set term. This calculator turns a deposit, a rate, and a term into the value at maturity and the dollars of interest earned. It accepts the rate either way banks quote it: as APY (annual percentage yield, which already includes compounding — A = P × (1 + APY)ᵗ) or as APR plus a compounding frequency (A = P × (1 + r/m)^(m·t), where m is compounding periods per year). Assumptions: interest stays in the CD and compounds until maturity, the rate is fixed for the full term, and results are pre-tax — CD interest is taxed as ordinary income in the year it is credited, even if you have not withdrawn it. Early withdrawals are penalized; see the FAQ before counting on access to the money.

Value at maturity

$10,450.00

Interest earned

$450.00

APY used

4.50%

Computed as A = P × (1 + APY)t over 1 year — APY already includes compounding, so no frequency input is needed. Assumes interest stays in the CD until maturity. Withdrawing early triggers a penalty (commonly several months of interest), and interest is taxable as ordinary income in the year it is credited.

How to use the cd interest calculator

  1. Enter your deposit amount and the CD term in months or years.
  2. Choose how the rate is quoted: APY (what US banks advertise) or APR with a compounding frequency (daily, monthly, quarterly, or annually).
  3. Read the maturity value, interest earned, and the effective APY the math implies.
  4. Compare offers by APY only — two CDs with the same APY pay the same regardless of compounding frequency.

The two formulas, worked through

APY mode: maturity = P × (1 + APY)ᵗ with t in years. The compounding frequency is irrelevant because APY is defined as the one-year growth factor after compounding. APR mode: maturity = P × (1 + r/m)^(m·t). For $10,000 at 4.40% APR compounded monthly for 2 years: r/m = 0.044/12 = 0.003667, m·t = 24, so maturity = 10,000 × (1.003667)²⁴ ≈ $10,918 and the effective APY is (1.003667)¹² − 1 ≈ 4.49%. Daily compounding of the same APR nudges the APY to about 4.50% — frequency matters far less than people assume once rates are in normal ranges. The only number worth comparing across banks is APY.

Interest on $10,000 by term and APY

Term3.50% APY4.50% APY5.50% APY
6 months$173$222$271
1 year$350$450$550
3 years$1,087$1,412$1,742
5 years$1,877$2,462$3,070

Figures are P × (1 + APY)ᵗ − P, rounded to the dollar. Notice the compounding curvature: five years at 4.50% earns $2,462, not 5 × $450 = $2,250, because each year's interest itself earns interest in later years.

Pitfalls that cost real money

The quiet one is the auto-renewal trap: at maturity most banks give you a grace period of about 7–10 days, then roll the balance into a new CD of the same term at whatever rate is current — often far below promotional rates. Calendar the maturity date. The second is ignoring inflation and taxes together: a 4.50% APY with interest taxed at a 24% marginal rate nets about 3.42%, which a 3.5% inflation year almost fully erases. CDs protect principal, not purchasing power. If your horizon is long and the goal is growth rather than capital preservation, compare the math against a recurring investment plan with the investment goal calculator; if you carry credit-card debt, paying it down beats any CD — check the credit card interest calculator to see why a guaranteed 20%+ “return” from debt payoff dwarfs any deposit rate.

Frequently asked questions

What is the difference between APY and APR?

APR (or the nominal rate) is the simple annual rate before compounding; APY is what you actually earn after compounding is folded in. A CD paying 4.40% APR compounded daily yields (1 + 0.044/365)^365 − 1 ≈ 4.50% APY. US banks must advertise deposit products by APY under Regulation DD (Truth in Savings), which makes offers directly comparable: a 4.50% APY compounded daily and a 4.50% APY compounded monthly pay exactly the same dollars per year.

How much does a typical CD actually earn?

Worked example: $10,000 in a 12-month CD at 4.50% APY matures at 10,000 × 1.045 = $10,450 — $450 of interest. Stretch it out: $10,000 at 4.00% APY for 5 years grows to 10,000 × 1.04^5 = $12,166.53, or $2,166.53 of interest. An 18-month CD of $25,000 at 5.00% APY matures at 25,000 × 1.05^1.5 ≈ $26,898 — fractional years work fine in the formula because APY is an annualized growth rate.

What happens if I withdraw a CD early?

Banks charge an early-withdrawal penalty, almost always quoted as a number of months of interest — commonly around 3 months on short CDs and 6–12 months on multi-year terms, though every institution sets its own schedule. On some CDs the penalty can eat into principal if you exit before earning that much interest. The penalty is set in your account agreement, so read it before buying; if you might need the cash, a no-penalty CD or high-yield savings account trades a little yield for liquidity.

Is CD interest insured and is it taxable?

CDs at FDIC-member banks are insured up to $250,000 per depositor, per bank, per ownership category (NCUA provides equivalent coverage at credit unions), covering both principal and accrued interest within the limit. The interest is fully taxable as ordinary income at the federal level — the bank issues a 1099-INT for the year the interest is credited, not the year you cash out. There is no preferential capital-gains treatment, which is one reason CDs fit well inside IRAs.

Should I pick a longer CD for a higher rate?

Not automatically. Compare the marginal yield against the lock-up: if a 12-month CD pays 4.50% APY and a 5-year pays 4.00%, the longer CD only wins if you expect rates to fall and stay below 4% for years. A common middle path is a CD ladder — splitting the money across staggered maturities (say 1, 2, 3, 4, and 5 years) so a rung matures every year, letting you reinvest at current rates while keeping a higher blended yield than parking everything short.

Why does my bank's number differ slightly from this calculator?

Three usual causes. First, day-count: some banks compound on a 365-day basis, others 360, and leap years add a day. Second, rounding: banks credit interest in cents at each compounding event, while this tool computes the closed-form value. Third, term definitions: a "12-month" CD opened mid-month may accrue for 365–366 actual days. These effects move the result by pennies to a few dollars on typical balances — the APY-based figure here is the right number for comparing offers.

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