CD Calculator

What this calculator does

The CD calculator takes the three numbers the bank quotes (your initial deposit, the APY, and the term length) and returns the value of the CD at maturity, how much of that is interest, and an optional estimate of the early withdrawal penalty if you break the CD before maturity.

How the math works

Because APY is the effective annual rate, the future value of a CD is simply the initial deposit grown by (1 + APY) raised to the term in years. This avoids the double counting that can happen when a nominal rate is used along with a compounding factor.

If you have only a nominal rate, use the APY calculator to convert to APY first, then plug the APY into this CD calculator.

Term length

Common CD terms run from 3 months to 5 years, though longer terms exist. Enter the term in months or years using the unit toggle. The math is the same; the unit toggle just controls how you type the number.

Early withdrawal penalty

Banks charge a penalty if you break a CD before its term ends. The penalty is most often stated as a number of months of interest. The calculator translates that into a dollar value using your APY: penalty = principal × ((1 + APY)^(months ÷ 12) − 1).

A penalty on its own does not tell you what you would walk away with, because a CD broken early does not pay the maturity value. If you close a 12-month CD at month 6, you have earned roughly six months of interest, not twelve. That is why the calculator asks when you would withdraw before showing a net figure: it grows the deposit to the withdrawal month, then subtracts the penalty. Without a withdrawal month it shows the penalty estimate alone.

Real bank penalty rules can differ. Some compute the penalty on a daily-equivalent rate; some compute it only on interest already accrued; some have tiered penalty tables based on the term. A penalty can also be larger than the interest earned so far, which is how an early withdrawal can return less than the original deposit. Regulation DD requires your institution to disclose that a penalty may be imposed, how it is calculated, and the conditions for assessing it — that disclosure, not this estimate, governs your CD.

Worked example

Initial deposit $10,000, APY 4.5%, term 12 months, no early withdrawal penalty.

• Term in years: 12 ÷ 12 = 1
• Value at maturity: 10,000 × (1 + 0.045)^1 = $10,450.00
• Interest earned: 10,450 − 10,000 = $450.00

Now suppose you break that CD at month 6 and the bank's penalty is 6 months of interest:

• Balance at 6 months: 10,000 × (1 + 0.045)^(6 ÷ 12) ≈ $10,222.52
• Penalty: 10,000 × ((1 + 0.045)^(6 ÷ 12) − 1) ≈ $222.52
• You walk away with ≈ $10,000.00 — the penalty consumes the interest earned so far

Note that this is not the maturity value minus the penalty. Holding to maturity would have produced $10,450; withdrawing at month 6 never earns that amount in the first place.

Assumptions and limitations

• APY is treated as an effective annual yield. Regulation DD defines APY as a percentage rate reflecting the total amount of interest paid on an account, based on the interest rate and the frequency of compounding, for a 365-day period. The calculator therefore applies it directly and does not re-apply a compounding factor.
• Terms are converted as months ÷ 12, which is an approximation. Appendix A to Regulation DD calculates APY from the actual number of days in the term: APY = 100[(1 + Interest/Principal)^(365/days in term) − 1]. Inverting that gives a balance of P × (1 + APY)^(days ÷ 365), whereas this calculator uses P × (1 + APY)^(months ÷ 12). Those agree only when a month is treated as exactly 365 ÷ 12 ≈ 30.42 days. For accounts offered in multiples of months, Appendix A lets an institution use either the actual days or the days in an actual sequence of that many calendar months, so a 6-month term may be 181–184 days rather than 182.5. On a $10,000 deposit at 4.5% APY the difference is under about $2. Treat short and odd terms as model estimates, not as the amount a bank must credit.
• A single fixed rate for the whole term. Tiered, bump-up, step-up, callable, and variable-rate CDs are not modeled.
• No contributions, no renewal. One deposit, held to the entered term. Rollover at a different APY is not modeled.
• Penalty rules are generic. The months-of-interest estimate is a common convention, not your bank's formula.
• Pre-tax. No federal, state, or local tax is applied.

Sources

• Regulation DD § 1030.2, Definitions (CFPB) — defines annual percentage yield as a rate reflecting the total interest paid, based on the interest rate and compounding frequency, for a 365-day period. Basis for treating APY as the effective annual rate.
• Appendix A to Regulation DD, Annual Percentage Yield Calculation (CFPB) — gives the disclosure formula APY = 100[(1 + Interest/Principal)^(365/days in term) − 1] and defines “days in term” as the actual number of days in the term, with a permitted alternative for accounts offered in multiples of months. This is the authority for the term exponent and for treating months ÷ 12 as an approximation.
• Regulation DD § 1030.4, Account disclosures (CFPB) — requires disclosure that a penalty may be imposed for early withdrawal, how it is calculated, and the conditions for its assessment, plus the maturity date for time accounts.
• FDIC, Deposit Insurance — standard coverage of $250,000 per depositor, per FDIC-insured bank, per ownership category, with certificates of deposit among the covered products.
• NCUA, Share Insurance Coverage — $250,000 share insurance at federally insured credit unions, covering time deposits such as share certificates.
• IRS Topic no. 403, Interest received — lists interest on certificates of deposit as taxable interest and states that most interest credited to an account you can withdraw from without penalty is taxable in the year it becomes available.

CD vs other savings options

A CD locks in a rate for a fixed term, which is useful when rates are high and you can spare the principal for the full term. A high-yield savings account keeps the flexibility but has a variable rate. A money market account is in between. The right choice depends on your time horizon and how much liquidity you need.

For longer-term retirement money, see the 401k calculator and Roth IRA calculator. For modeling broader compounding scenarios with monthly contributions, use the compound interest calculator.

Common mistakes

• Treating APY as a nominal rate and adding compounding on top. APY already includes compounding.
• Comparing two CDs at the same nominal rate but different compounding. Convert both to APY first.
• Ignoring the early withdrawal penalty. If your goal might need the cash early, model the penalty so the effective return is realistic.
• Subtracting an early withdrawal penalty from the maturity value. Breaking a CD early earns only the interest accrued up to that point, so start from the balance on the withdrawal date instead.
• Forgetting taxes. The IRS treats CD interest as taxable interest, so the pre-tax figures here are not what you keep.
• Assuming a CD will roll over at the same rate. At maturity, the bank may offer a different APY or roll into a different product.

Related tools

• APY calculator for converting a nominal rate plus compounding into APY.
• Savings calculator for an ongoing savings plan with optional monthly contributions and goal-oriented modes.
• Simple interest calculator for non-compounding interest math, useful for short notes and certain promotional offers.
• Compound interest calculator for projecting balances with optional monthly contributions.
• 401k calculator for employer-sponsored retirement projections with salary growth and employer match.
• Roth IRA calculator for an individual after-tax retirement account.
• Simple interest vs compound interest explains the two formulas, the difference in growth, and why CD math is compound.