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Compound Interest Calculator

See ending balance, contributions, modeled interest, APY, and year-by-year growth, then adjust contribution timing or growth only when the scenario needs it.

Starting balance

Regular contribution

Annual rate (%)

Years

Monthly compounding·Monthly contribution

Projected ending balance

—

Updates as you type.

—Total contributed

—Modeled growth

—Effective annual yield

Starting balanceAdded moneyGrowth

—

Growth over timeBalance vs contributed

Compounding & contribution options

Compounding frequency

Contribution frequency

Annual contribution increase (%)

Rate sensitivity (± points)

Contribution timing

Rate sensitivity & projection details

—Lower-rate balance

—Base balance

—Higher-rate balance

—Exact doubling time

—Ending / starting balance

—Contribution periods

Save a scenario in this browser

Scenario name

This is deterministic compound-interest math, not a prediction of investment returns or future savings rates. Taxes, fees, volatility, and account rules are not modeled.

Independent formula & assumption audit

Recalculate the core payment or growth path with a separate browser-local formula layer. It reads the existing inputs, does not fetch live rates, and does not replace the primary calculator.

Set the finance assumptions above, then refresh this audit.

Formula audit ready. User-entered assumptions only.

Core borrowing, saving & investing workflows

Start with the broad calculator that matches the decision, then move to a specialist only when the loan structure, cash flow, tax treatment, debt strategy or savings goal genuinely changes.

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How to use the Compound Interest Calculator

Start with the balance, regular contribution, annual rate, and years. The projected ending balance updates immediately. Open Compounding & contribution options only when you need a different compounding schedule, contribution timing, contribution growth, or rate-sensitivity comparison.

Read the result at a glance

The main result separates the money contributed from modeled compound growth and plots both over time. This makes it easier to see whether the ending balance is being driven mostly by your own deposits, time, or the assumed rate.

Modeling limits

This is deterministic compound-interest math. It does not predict future market returns, savings rates, taxes, fees, volatility, or account rules.

Compound interest formula

Without recurring contributions, compound growth follows the standard future-value formula below. When contributions are enabled, the calculator applies each contribution according to the selected timing and compounds the running balance over the modeled periods.

A = P × (1 + r ÷ n)^(n × t)

P is the starting balance, r is the annual rate as a decimal, n is compounds per year, and t is years.

Example

$10,000 growing at 5% compounded annually for 10 years, with no added contributions, becomes about $16,289. The difference from the starting $10,000 is modeled interest.

Useful next calculations

Savings calculator Investment calculator APY calculator Simple interest