Use this CD calculator to estimate how much your certificate of deposit will be worth at maturity, how much interest you earn, and what happens if you withdraw early with a penalty.
Advanced options
How to use our CD Calculator
- Enter your Initial deposit (USD) (how much you put into the CD).
- Pick Rate type: choose APY if your bank lists an annual percentage yield, or APR if it lists a simple annual rate.
- Enter the Interest rate (percent) exactly as shown by your bank (example: 4.00).
- Enter the CD term (months) (example: 12 for 1 year, 60 for 5 years).
- Choose Compounding frequency (how often interest gets added to the balance).
- Open Advanced options if you want to change how interest is handled (reinvest vs payout), show a schedule by month or year, estimate an early-withdrawal penalty, or estimate after-tax results.
- Click Calculate.
- Read Value at maturity and Total interest earned for the full-term estimate, and use Effective annual yield used to double-check you entered APY vs APR correctly.
- If you turned on early withdrawal, check Value at withdrawal (before penalty), the Estimated early withdrawal penalty, and your Estimated amount you receive (after penalty).
- If you turned on after-tax mode, review the after-tax interest and after-tax maturity value and adjust tax rates if needed.
Definitions
CD (certificate of deposit): A bank account where you agree to leave money for a set time in exchange for interest.
Principal: Your starting deposit (your original money).
APY (annual percentage yield): The yearly return including compounding.
APR (annual percentage rate): A simple yearly rate before compounding.
Compounding: When interest is added to the balance so future interest can be earned on it.
Maturity: The end of the CD term.
Early-withdrawal penalty: A fee (often lost interest) charged if you take money out before maturity.
Marginal tax rate: The percent of tax you pay on your next dollar of income (used here as a simple estimate for taxing interest).
Methodology
Inputs and setup
This calculator accepts a deposit (principal), a rate type (APY or APR), a rate percent, a term in months, and a compounding frequency (daily, monthly, quarterly, semiannual, or annual). Term in years is computed as term_years = term_months / 12.
Convert APY and APR
If you choose APR, the calculator converts it to an effective annual yield (APY) based on the chosen compounding frequency.
apy_decimal = (1 + apr_decimal/compounds_per_year)^(compounds_per_year) - 1
If you choose APY, the calculator converts that APY into an equivalent APR for the chosen compounding frequency (so the schedule and partial-term math stay consistent with the APY you entered).
apr_equiv_decimal = compounds_per_year * ( (1 + apy_decimal)^(1/compounds_per_year) - 1 )
The output Effective annual yield used (percent) is this annualized yield after conversion. It helps you spot the common mistake of entering an APY when the tool expects an APR (or the other way around).
Maturity value (reinvest vs payout)
Reinvest (compound) means interest stays in the CD and earns interest too. Growth uses a per-compounding-period rate and supports partial months by splitting into full periods plus a prorated leftover fraction.
balance = principal*(1+apr_equiv/compounds)^(floor(compounds*months/12)) * (1 + (apr_equiv/compounds)*fractional_part)
Here, fractional_part is the fractional part of (compounds*months/12). This avoids pretending you earned a full extra compounding period when the term includes a partial period.
Payout (no reinvest) means interest is paid out instead of staying in the CD, so the balance does not compound. This is modeled as simple interest on the original principal.
maturity_value = principal + principal * simple_rate_annual * (term_months/12)
When Rate type is APY and Interest handling is Payout, simple_rate_annual is approximated using the entered APY (because APY is normally defined with compounding). If your bank provides an APR or a simple interest rate for payout CDs, use APR for a cleaner estimate.
Total interest
total_interest = maturity_value - principal
Balance schedule (monthly or yearly)
The schedule shows period-by-period starting balance, interest earned, and ending balance. Monthly is usually easiest for short terms; yearly is easier for long terms. When compounding is daily, the schedule uses an approximation for month length while keeping the final maturity value consistent with the main growth calculation.
Early withdrawal estimate (optional)
If enabled, the calculator first estimates the value after holding the CD for months_held (using the same reinvest vs payout logic as above). Then it estimates the penalty using the penalty style you select.
penalty = penalty_days * (apr_equiv_decimal/365) * principal
penalty = penalty_months * (apr_equiv_decimal/12) * principal
net_proceeds = value_at_withdrawal - penalty
If net_proceeds would be negative, the calculator shows N/A for the net amount and tells you to re-check your penalty settings, because you cannot receive a negative payout.
After-tax estimate (optional)
If after-tax mode is On, the calculator estimates taxes on interest using your marginal federal and state rates (a simplified estimate).
tax = total_interest*(fed_rate+state_rate)/100
after_tax_interest = total_interest - tax
after_tax_maturity = principal + after_tax_interest
Validation and edge cases
The calculator blocks invalid inputs (like a blank rate, non-numeric text, principal less than or equal to 0, term less than or equal to 0, or months_held greater than or equal to term_months). It also stops if any step would create NaN or Infinity. Money results are displayed with commas and cents, while internal math keeps full precision.