Formulas and sources
Each formula this calculator uses, where it comes from, and what it leaves out. "How it works" shows the same formula with your own numbers.
Value at maturity, interest reinvested
Simple mode, when Interest Payout is Reinvested
- A
- value at maturity
- P
- principal
- r
- the yearly interest rate, in percent: 4.5 for 4.5%
- n
- compounding periods per year: 365, 12, 4, 2 or 1
- t
- term in years; a term in months counts as months ÷ 12
A term typed in years counts as whole months when it falls within 0.4 of a whole month, so 1.1 years is 13 months.
Source: Standard formula; no single publisher.
Value at maturity, interest paid out
Simple mode, when Interest Payout is Paid Out
- A
- the principal plus all the interest paid out
- P
- principal
- r
- the yearly interest rate as a decimal: 4.5% is 0.045
- t
- term in years
Paid-out interest does not compound, so it is simple interest. Here r is a decimal, where the reinvested formula divides a percent by 100 inside the brackets.
Source: Standard formula; no single publisher. The Effective Rate (APY) shown is the stated rate, which Regulation DD allows for a CD over one year that does not compound and requires interest to be paid out at least yearly [1]. For a shorter CD, Regulation DD's formula gives a higher APY.
Effective APY
Every mode
- APY
- annual percentage yield, as a fraction: 0.0512 is 5.12%
- r
- the yearly interest rate, in percent
- n
- compounding periods per year: 365, 12, 4, 2 or 1
Shown as the Effective Rate (APY), in percent to two decimal places. Add-on deposits do not change it. In Ladder mode, rungs with different rates show a range.
Source: Based on Regulation DD's APY formula, Appendix A, Part I.A [1]. With daily compounding, this formula and Regulation DD's agree for a term of any length. For other frequencies, a bank's APY can differ slightly on terms other than one year, most on short ones. Regulation DD has banks round the APY to two decimals [2].
Value at maturity with add-on deposits
Add-On mode
- A
- value at maturity
- P
- opening deposit
- r
- the yearly interest rate, in percent: 4.5 for 4.5%
- n
- compounding periods per year: 365, 12, 4, 2 or 1
- t
- term in years
- D
- deposit added each period
- f
- deposits per year: 12, 4 or 1
- k
- the deposit's number: 1 for the first, up to the last whole period in the term
- APY
- the effective annual rate as a decimal: (1 + r ÷ n ÷ 100)^n - 1
Each deposit is made at the end of its period and grows for the rest of the term. A term shorter than one deposit period adds none. Interest Payout does not apply in this mode.
Source: Standard formula; no single publisher.
Ladder value at maturity
Ladder mode
- Total Maturity Value
- the sum of every rung's value at its own maturity
- P
- the principal you enter, split equally across the rungs
- N
- number of rungs, 2 to 10
- r
- the rung's own yearly rate in percent, or the Interest Rate when it has none
- n
- compounding periods per year: 365, 12, 4, 2 or 1
- t
- the rung's own term in years: rung i matures at i × the longest term ÷ N
Every rung compounds: Interest Payout is ignored in this mode. Matured rungs are not reinvested.
Source: Standard formula; no single publisher. The ladder layout is CalcTrail's own.
Value after an early withdrawal
Penalty mode
- Value After Penalty
- what comes back: principal plus interest earned, less the penalty
- Principal
- the amount deposited
- rate
- the yearly interest rate as a decimal: 4.5% is 0.045
- Penalty months
- the Penalty (Months of Interest) field: months of simple interest
The penalty is simple interest on the principal at the stated rate, not the APY. It comes out of the interest earned first, then out of principal. The interest earned by the withdrawal month follows the Interest Payout setting and counts only the months held.
Source: Based on the "months of interest" form in Regulation DD's model clause [3]. The Federal Reserve's Regulation D sets a minimum, with a few exceptions: seven days' simple interest on money withdrawn within six days of a deposit or of an earlier partial withdrawal [4]. The Office of the Comptroller of the Currency says federal law sets no maximum [5]. Your bank sets the actual penalty.
Sources
- Consumer Financial Protection Bureau. 12 CFR part 1030 (Regulation DD), Appendix A: Annual Percentage Yield Calculation, Part I. eCFR, current as of October 1, 2026.
- Consumer Financial Protection Bureau. 12 CFR 1030.3 (Regulation DD): General disclosure requirements, paragraph (f)(1), rounding. eCFR, current as of October 1, 2026.
- Consumer Financial Protection Bureau. 12 CFR part 1030 (Regulation DD), Appendix B: Model Clauses and Sample Forms, Model Clause B-1(h)(ii), early withdrawal penalties. eCFR, current as of October 1, 2026.
- Board of Governors of the Federal Reserve System. 12 CFR 204.2 (Regulation D): Definitions, paragraph (c)(1)(i) and footnote 1, time deposit. eCFR, current as of October 1, 2026.
- Office of the Comptroller of the Currency. What are the penalties for withdrawing money early from a CD? HelpWithMyBank.gov, last reviewed April 2021.
What this calculator does not cover
- This values one CD, or a ladder of them, at the rates you enter. It does not model a rate that changes during the term, a callable CD (one the bank can redeem early), or automatic renewal at a new rate.
- It leaves out tax on interest, a brokered CD (one bought through a brokerage) sold before maturity, and penalties other than months of simple interest.
- This tool counts a month as a twelfth of a year, so six months of daily compounding is 182.5 days. A bank counts days, so its interest can differ slightly: $1,000 at 6.00% compounded daily earns $30.45 here and $30.37 over 182 days.
Sources checked on .