Money & finance
Compound interest calculator
Estimate how a starting balance and regular contributions could grow over time. Choose compounding frequency and contribution timing, with calculations kept in your browser.
Works locally in your browser
How this tool works
Compound interest adds each interest amount to the balance that later interest is calculated from. This calculator projects that repeated process and shows how much of the ending balance comes from money contributed versus estimated interest.
You can model an initial amount alone or add monthly, quarterly, or annual contributions. The result includes an effective annual rate and a year-by-year schedule, and every calculation remains inside your browser.
Inputs and definitions
- Starting amount is the balance available before the first contribution or compounding period. It is included in total contributions.
- Annual interest rate is a nominal percentage, such as 7 for 7%. A negative assumption is allowed and produces a warning because it reduces the projected balance.
- Term combines whole years with 0 to 11 additional months, from one month up to 100 years.
- Compounding frequency controls how often earned interest is added. Daily means 365 equal periods per year, not the actual dates used by a financial institution.
- Recurring contribution may be scheduled monthly, quarterly, or annually at the beginning or end of each period. An annual increase changes contributions only after a completed year.
Select the number format before entering values. The currency selector changes the symbol and display rules only; it does not convert amounts or retrieve exchange rates.
Methodology
future value = principal × (1 + nominal annual rate / periods per year)^(periods per year × years)When contributions are present, the calculator uses an event timeline instead of assuming contribution and compounding frequencies match. Beginning contributions are added before their period can earn interest; end contributions are added after that period's interest.
Calculations retain decimal working precision. The schedule derives each interest row from the exact change in balance after contributions, so the displayed summary and exported raw rows reconcile before presentation rounding.
Assumptions
- The nominal rate and chosen frequency remain constant for the full term.
- Each scheduled contribution occurs in full and the annual contribution change is applied after each completed year.
- All amounts use one currency and no exchange-rate conversion is performed.
Worked examples
Grow 1,000 for two years at 10% annually
Start with 1,000, make no recurring contributions, and compound a 10% nominal annual rate once per year for two years.
Complete the first annual period
Ten percent of 1,000 is 100, giving a first-year balance of 1,100.
Compound the new balance
The second year's 10% is calculated on 1,100, adding 110 rather than the first year's 100.
The future balance is 1,210: total contributions remain 1,000 and estimated interest is 210.
Separate contributions when the rate is zero
Start with 1,000 and add 100 at the end of every month for one year while the annual rate is 0%.
Count scheduled contributions
Twelve monthly contributions add 1,200 to the 1,000 starting principal.
Separate interest
With a zero rate, the estimated interest remains zero regardless of compounding frequency or contribution timing.
The future balance and total contributions are both 2,200, and estimated interest is zero.
Limitations and common mistakes
This is a mathematical projection, not a forecast or financial advice. Actual savings and investments can have variable returns, contribution interruptions, product-specific posting rules, minimum balances, and loss of principal.
Taxes, fees, inflation, withdrawals, employer matching, and product guarantees are excluded. Account providers may calculate or credit interest on dates that differ from this deterministic estimate timeline.
Frequently asked questions
What is the difference between nominal and effective annual rate?
A nominal annual rate states the yearly rate before the within-year compounding effect. The effective annual rate measures the one-year change produced by applying the selected frequency.
Should contributions be at the beginning or end?
Choose the timing that matches when money is actually added. Under a positive rate, a beginning contribution can earn during that period and will normally finish higher than the same end contribution.
Why might my bank or investment result differ?
Real products can use dated transactions, changing rates, fees, taxes, business-day rules, and different day-count or interest-crediting conventions. This calculator uses the explicit simplified assumptions shown above.
Does selecting another currency convert the projection?
No. The selector changes formatting only. Use values in one consistent currency and handle any currency conversion separately.
Sources
- Compound Interest Calculator — Investor.gov, U.S. Securities and Exchange Commission (accessed )
- How does compound interest work? — Consumer Financial Protection Bureau (accessed )
Method and content record
The method, examples and limitations describe how this tool works. Recorded checks do not establish independent professional review.
Record attribution, date and versions
Record attribution: ToolsOrigin calculation review; introduction guidance checked by Codex.
Record date: .
Content version 1.0.1. Engine version 1.0.0.