Compound Interest Calculator
Convert equivalent rates across compounding frequencies or project investment growth over time.
Currency formatting only; amounts are not converted. Returns are estimates, not guarantees.
Convert compounding rates
Compare nominal interest rates across compounding frequencies while keeping the same effective annual return.
Equivalent-rate math excludes fees, taxes, and lender-specific conventions.
Investment growth assumptions
Contributions are added at each month end; a partial final month is counted pro-rata. Weeks use 52 weeks per year and are approximate. Taxes, fees, and investment risk are not included.
Growth over time
Projected value compared with cumulative contributions.
Ending balance share
Annual growth schedule
| Year | Contributions | Growth | Ending value |
|---|
Detailed Breakdown
The converter compares equivalent rates; the separate growth projection estimates a balance from a deposit and regular contributions.
Inputs
Set the initial investment, monthly contribution, annual nominal rate, time horizon, and how often interest compounds. Contributions are added at each month end. Currency selection changes display formatting only.
Rate conversion
For input nominal rate r compounded
m times yearly, the effective annual factor is
(1 + r/m)m. For output frequency q, the equivalent nominal rate
is q * [(1 + r/m)m/q - 1].
Reading the results
Future value is the projected ending balance. Contributions include the initial investment plus all monthly deposits; growth is the difference between future value and total contributions. The chart compares projected value with deposits made.
Assumptions and limits
The assumed rate stays constant and deposits arrive at month end. Taxes, fees, inflation, withdrawals, changing returns, and investment risk are excluded. Market returns are uncertain; this projection is not a promise of performance.
Examples
A nominal annual rate of 6% compounded monthly has an effective annual yield of about 6.17%. In the separate growth projection, monthly deposits are added at month end and grow using the selected rate assumption.
FAQ
What is the difference between nominal rate and effective yield?
The nominal rate is the quoted annual rate before accounting for compounding. Effective annual yield reflects the effect of compounding over a full year.
When do monthly deposits start earning?
Deposits are modeled at month end, so each deposit begins earning the assumed return in the following month.
Are projected returns guaranteed?
No. A constant rate is only a planning assumption; actual investment returns fluctuate and may be negative.
Related Calculators
- Future Value Calculator — project a lump sum or periodic deposits.
- Investment Calculator — model an initial amount and contributions.
- Savings Calculator — estimate savings growth and interest.
Internal links: compare growth methods with the Future Value Calculator and contribution planning in the Investment Calculator.