investment calculator

CD Calculator

The CD Calculator estimates how a fixed starting deposit could mature over a selected term. Enter the deposit, annual rate, compounding choice, years, months, and marginal tax-rate assumption to see gross maturity value, total interest, estimated tax due, after-tax balance, effective annual yield, first-month interest, and first-year interest.

Result

Ending balance: $11,576.25
Total interest: $1,576.25
Estimated tax due: $0.00
After-tax end balance: $11,576.25
After-tax interest: $1,576.25
Effective annual yield: 5.00%
First month interest: $40.74
First year interest: $500.00
What this means: Fixed-rate CD estimate before early withdrawal penalties or account fees.

Scenario nameNotes

Save this result, then use saved scenarios to switch between assumptions.

How the CD Calculator works

Use this calculator when the core question is a fixed-term deposit with no additional deposits or withdrawals before maturity. Use the savings calculator when recurring deposits or contribution increases matter, the interest calculator when timing and inflation inputs matter, and the interest-rate calculator when you need to solve for a rate instead of entering one.

The calculator converts the entered annual interest rate into an effective monthly rate from the selected compounding option. Annual compounding uses the twelfth root of the annual growth factor; continuous compounding uses e^(rate / 12) - 1. It rounds years * 12 + months to whole term months, grows the initial deposit to gross maturity value, calculates total gross interest, applies the marginal tax-rate assumption to gross interest after maturity, then reports after-tax balance, effective annual yield, first-month interest, and first-year interest.

CD Calculator formula

This formula page covers the app's CD Calculator: a fixed starting deposit, a user-entered annual interest-rate assumption, a compounding choice, a term entered in years and months, and a simple marginal-tax-rate estimate. It models gross maturity first, then subtracts estimated tax from total gross interest. It does not price early-withdrawal penalties, changing rates, renewal choices, account fees, deposit-insurance coverage, provider terms, or jurisdiction-specific tax rules.

m = (1 + r / n)^(n / 12) - 1; continuous: m = e^(r / 12) - 1; MV = P * (1 + m)^T; Tax = (MV - P) * tax

The annual percentage rate is converted to an effective monthly rate, the deposit is grown for the rounded number of term months, and estimated tax is calculated from total gross interest.

Symbol	Meaning	How this page uses it
MV	Maturity value	The gross ending balance before the tax-rate estimate is subtracted.
P	Initial deposit	The starting deposit entered on the calculator.
r	Nominal annual rate as a decimal	The Interest rate field divided by 100, so 5 percent becomes 0.05.
n	Compounding periods per year	The period count implied by the selected compounding frequency, such as 1 for annual, 4 for quarterly, or 12 for monthly.
m	Effective monthly rate	The rate applied to the deposit for each month after converting from the selected compounding frequency.
T	Term months	The deposit length converted from years and months into a rounded whole number of months.
I_gross	Total gross interest	Maturity value minus the initial deposit.
tax	Marginal tax-rate assumption	The user-entered percentage applied to gross interest. It is not an official tax calculation.
Tax	Estimated tax due	Total gross interest multiplied by the tax-rate assumption, calculated after gross maturity.
I_net	After-tax interest	Gross interest minus the estimated tax due.
MV_net	After-tax end balance	Initial deposit plus after-tax interest.
EAY	Effective annual yield	The annualized rate implied by the effective monthly rate, returned as a percentage.

Step by step

Convert the entered annual percentage rate into decimal form by dividing by 100.
Convert the selected compounding frequency into an effective monthly rate. Annual compounding uses the twelfth root of the annual growth factor for monthly term steps; continuous compounding uses e raised to the annual decimal rate divided by 12, minus 1.
Convert the entered years and months into total term months. The implementation rounds that term to a whole month count.
Grow the initial deposit by the effective monthly rate for the whole term to get gross maturity value.
Subtract the initial deposit from gross maturity value to get total gross interest.
Multiply total gross interest by the user-entered marginal tax-rate assumption to estimate tax due.
Subtract estimated tax due from gross interest to get after-tax interest, then add that to the initial deposit for after-tax end balance.
Calculate effective annual yield from the same monthly rate by compounding it for 12 months.
Calculate first-month interest from the initial deposit and monthly rate. Calculate first-year interest by growing the initial deposit for up to the first 12 term months.
Round currency and percent outputs for display after the full-precision calculation.

Worked example

Default example: $10,000 at 5 percent annually for 3 years

The default calculator inputs use a $10,000 initial deposit, a 5 percent annual rate, annual compounding, a 3-year term, 0 extra months, and a 0 percent marginal tax-rate assumption.

Convert 5 percent to 0.05.
With annual compounding, the monthly rate is the twelfth root of 1.05 minus 1, or about 0.4074 percent per month.
Run 36 monthly term steps because the deposit length is 3 years and 0 months.
Grow $10,000 by that monthly rate for 36 months to get a gross maturity value of $11,576.25.
Gross interest is $11,576.25 minus $10,000, or $1,576.25.
Because the tax-rate assumption is 0 percent, estimated tax due is $0 and after-tax interest is also $1,576.25.
The first-month interest is about $40.74, and the first-year interest is $500.00 because the annual compounding choice preserves the 5 percent annual yield for a full year.

This is a deterministic fixed-rate CD estimate from the entered assumptions. It is not a bank quote, tax answer, deposit-insurance determination, or prediction of what a provider will offer.

Assumptions and what this calculator ignores

Geographic scope: works globally. The math is currency-agnostic, so enter amounts in your own currency; local taxes, fees, and product rules are not included.

The initial deposit stays in the CD for the full entered term, and the entered rate and compounding choice stay fixed for the whole estimate.
The tax-rate input is a simple user-entered assumption applied to total gross interest after maturity. The calculator does not reduce reinvested interest each period and does not calculate official tax reporting, withholding, allowances, account wrappers, original issue discount, state tax, or local rules.
The calculator does not pull live APY, AER, provider quotes, renewal terms, promotional terms, account fees, early-withdrawal penalties, call features, brokered-CD rules, minimum balances, deposit-insurance coverage, inflation, or personal circumstances. Results remain educational estimates rather than financial, tax, legal, lending, investment, provider, or regulated advice.

What this formula does not include

The interest rate is a user-entered assumption, not a live CD rate, advertised APY, AER, provider quote, or renewal offer.
The calculator models gross maturity first and subtracts estimated tax from total gross interest. It does not compound after-tax interest each period.
The independent comparator can handle taxed CD examples differently by reducing reinvested interest each period, so positive-rate taxed scenarios are not exact like-for-like comparisons.
The tax-rate field is a simple user-entered assumption and does not apply official allowances, reporting timing, account wrappers, original issue discount rules, or jurisdiction-specific treatment.
No early-withdrawal penalty, changing rate, promotional period, call feature, brokered CD rule, renewal instruction, account fee, or minimum-balance rule is modeled.
No deposit-insurance limit or bank eligibility check is performed.
Currency and percent outputs are rounded after the formula result is calculated.

Common mistakes to avoid

Treating the entered interest rate as an advertised APY or provider quote. The calculator only uses the rate you type and shows an effective annual yield from that internal monthly-rate conversion.
Reading Estimated tax due as an official tax bill. It is a flat percentage of gross interest in this model and may differ from real account, reporting, or jurisdiction-specific treatment.
Ignoring term and product rules. Early-withdrawal penalties, renewal defaults, call features, brokered-CD terms, fees, and deposit-insurance limits can change the real-world result but are not calculator inputs.

Key terms

Gross maturity value: The ending balance before the tax-rate estimate is subtracted. The calculator grows the initial deposit first, then calculates estimated tax from total gross interest.
Effective annual yield: The annualized yield implied by the calculator's effective monthly rate. It helps explain the compounding assumption, but it is not a provider APY disclosure or product quote.
Marginal tax-rate assumption: The percentage applied to gross interest in this estimate. It is a simple scenario input, not an official tax rule, tax filing result, or personal tax answer.

Frequently asked questions

How is the CD's after-tax return estimated?

The calculator grows the deposit to gross maturity value first, then applies your marginal tax rate to the total gross interest in one step: tax = (maturity value − principal) × rate. It does not reduce each period's credited interest. That ordering matters - a comparator that taxes interest as it accrues will show slightly different after-tax figures, which the validation notes on this page call out explicitly.

What is the effective annual yield output on this CD estimate?

It converts your nominal rate and chosen compounding frequency into the single annually-compounded rate that would produce the same growth - useful for comparing a monthly-compounding CD against an annual one on equal footing. It is computed from the entered assumptions, so it is not the same as a bank's advertised APY, which reflects the institution's own compounding and crediting rules.

Can I model a CD term that is not a whole number of years?

Yes. The term is entered as years plus months - 18 months is years 1, months 6 - and the simulation converts the whole term to months with your compounding choice applied. First-month and first-year interest are reported separately so you can sanity-check the growth path. Early-withdrawal penalties, callable features, and renewal rates are not modeled; those are provider-specific terms.

Methodology, sources, and disclaimer

This calculator is an original fixed-deposit maturity model with a years-plus-months term, selectable compounding, and tax applied once to total gross interest at maturity, validated by deterministic fixtures, edge cases, and rounding policy tests. It is not copied from a single source.

Fixtures pin gross maturity, tax-at-maturity ordering, and the effective-annual-yield conversion; the notes document where period-by-period tax treatments diverge. The result remains an educational estimate, not a bank CD quote or a deposit-insurance determination.

Formula version 2026.05.22-generic-cd-maturity. The version marks the calculation logic and validation fixture set used for this estimate.

CFPB Regulation DD Appendix A should be used before copy discusses US annual percentage yield calculations, advertised APY terminology, time-account disclosure assumptions, bonuses, stepped rates, tiered rates, or product-specific account-yield claims.
IRS Topic 403 and relevant state or local tax-authority materials should be used before copy discusses US taxable interest, certificate-of-deposit tax reporting, withholding, original issue discount, tax-exempt interest, state tax, or personal tax outcomes.
FDIC, NCUA, FSCS, and relevant local deposit-protection sources should be used before copy discusses insured-bank or credit-union CD coverage, protected-balance limits, ownership categories, bank eligibility, failed-bank treatment, or jurisdiction-specific deposit protection.
SEC Investor.gov, FINRA, bank/provider disclosures, deposit-broker materials, and relevant local regulators should be used before copy discusses brokered CDs, callable CDs, early-withdrawal penalties, renewal defaults, minimum balances, account fees, promotional rates, liquidity, issuer checks, product risks, or provider-specific terms.

Results are educational estimates, not advice. Read the full disclaimer.

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