Interest Profit Calculator
See how much interest your money earns with compounding. Enter the principal, annual rate, years, and compounding frequency: the tool reports the final amount and interest earned, compares all five compounding frequencies for your exact inputs, and adds the effective annual rate, the Rule of 72, and a year-by-year schedule. Here “profit” means interest earned on one lump sum: there are no ongoing deposits in this model.
Illustration of compounding math. Real investments carry risk, fees, and taxes that this tool does not model.
Quick Answer
$10,000 at 6% for 10 years, compounded monthly, grows to $18,193.97: interest earned is $8,193.97, against $6,000.00 from simple interest. The effective annual rate is 6.1678%, and the same inputs compounded daily would reach $18,220.29. The calculator above is pre-filled with this exact example.
Key takeaways
- Interest earned is the final amount minus the principal. Everything else in the result (effective rate, Rule of 72, simple-interest baseline) is a way of judging that one number.
- Compounding frequency is a small lever: on the worked example, daily beats annual by $311.81 over ten years. Rate and time are the big levers.
- Compare accounts by effective annual rate, not the nominal rate: 6% compounded daily is really 6.1831% a year.
- The currency selector changes only the symbol printed. It never converts the amounts.
- Quick Answer
- How to use the interest profit calculator
- The compound interest formula
- Worked example: $10,000 at 6% for 10 years, every frequency
- Effective annual rate: the honest comparison
- The Rule of 72, and its limits
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the interest profit calculator
Enter one lump sum, its annual rate, and the years it stays invested, choose how often interest compounds, and click Calculate. Results stay hidden until you click.
- Principal: the single starting amount. There is no deposit field on purpose: this page prices one lump sum. If you add money every month, you need a contributions model, not this one.
- Annual interest rate: the nominal rate. A 0% rate is accepted and returns your principal unchanged, with no Rule of 72 line, because money at 0% never doubles.
- Time: years, fractions allowed. The final amount always uses your full entry; only the year-by-year schedule is limited to whole years and capped at 30 rows.
- Compounding frequency: how often interest joins the balance. Whatever you pick, the result also runs the other four frequencies on the same inputs and marks yours.
- Currency: a display symbol only ($, €, £, ₹, ¥). €2,000 at 4% for 5 years quarterly gives €2,440.38 by exactly the same numbers as the dollar run.
Working the other direction, from a target amount back to the rate or principal that produces it, is the job of the backward compound interest calculator. For day-count compounding on a balance you check often, the daily compound calculator focuses on that single frequency.
The compound interest formula
A = P × (1 + r/n)nt: the principal, times one plus the periodic rate, raised to the total number of compounding periods. Interest earned is A minus P.
Interest earned = A − P
Effective annual rate = (1 + r ÷ n)n − 1
P = principal, r = annual rate as a decimal, n = compounding periods per year, t = years
Each period, the interest just earned joins the principal and starts earning interest itself. That is the whole mechanism, and it is why the gap against simple interest widens with time: simple interest pays P × r × t on the original sum forever, while compounding pays on a growing balance. The formula assumes a fixed rate and no withdrawals, the same assumptions the Investor.gov compound interest calculator states for its own projections.
Worked example: $10,000 at 6% for 10 years, every frequency
The pre-filled run is $10,000 at 6% for 10 years. The table below is the tool’s own frequency comparison for those inputs, with the interest earned and the effective annual rate for each row. Every figure is a verified run of the calculator above.
| Frequency | Final amount | Interest earned | Effective annual rate |
|---|---|---|---|
| Annual | $17,908.48 | $7,908.48 | 6.0000% |
| Semi-annual | $18,061.11 | $8,061.11 | 6.0900% |
| Quarterly | $18,140.18 | $8,140.18 | 6.1364% |
| Monthly (the pre-filled run) | $18,193.97 | $8,193.97 | 6.1678% |
| Daily | $18,220.29 | $8,220.29 | 6.1831% |
Read the table as extra interest over annual compounding, and the frequency story gets honest fast. Daily compounding adds $311.81 over a decade on $10,000; most of that gain already arrives by quarterly compounding.
The monthly schedule inside the same run shows the curve bending upward: year 1 ends at $10,616.78, year 5 at $13,488.50, and year 10 at $18,193.97. The last year alone adds $1,057.00 of interest, against $616.78 in the first.
Effective annual rate: the honest comparison
The effective annual rate (EAR) is the true yearly yield after compounding: (1 + r/n)n minus 1. Two accounts quoting the same 6% nominal rate pay different yields if one compounds monthly (6.1678%) and the other daily (6.1831%), and the EAR is the number that exposes it.
This is the figure banks quote as APY on deposit accounts, which is why the effective interest rate calculator exists as a standalone conversion. Use it this way: if a product quotes a nominal rate, run it here and compare EARs; if it quotes an APY, that APY is already the EAR, so compare it directly against the EAR line in your result.
The Rule of 72, and its limits
Divide 72 by the annual rate to estimate the years needed to double your money: 72 ÷ 6 = 12 years at 6%. The tool prints this in every result at a positive rate, using your exact rate (at 3.25% it prints 22.2 years).
It is an approximation, most accurate for rates between about 6% and 10%, and it slightly overstates the doubling time at very low rates and understates it at very high ones. At 100% it prints 0.7 years, while annual compounding at 100% doubles in exactly 1 year. For the exact doubling time at your rate and frequency, the compound interest doubling time calculator solves the logarithm instead of estimating it.
What competing calculators miss
The big compound interest tools are broader than this page, and that breadth costs them the specific comparison this keyword asks for:
- Calculator.net Interest Calculator: adds annual and monthly contributions, tax rate, and inflation adjustment, with an accumulation schedule. Strength: a full savings planner. Gap for this question: with contributions switched on, the interest earned is no longer the profit on one principal, and its frequency comparison is buried inside a much larger form.
- Investor.gov Compound Interest Calculator: the authoritative US government tool, with monthly contributions and a growth chart. It solves the contribution case well, but it does not print an effective annual rate or a Rule of 72 doubling time next to the result, and it does not compare all five frequencies on your inputs.
- Omni Calculator Compound Interest: solves for any variable, including the rate or time needed for a target. Strength: flexibility. Gap: the answer-first layout gives one scenario at a time, so the frequency cost has to be found by re-running the tool five times.
- NerdWallet CD Calculator: purpose-built for certificates of deposit, quoting APY directly. Accurate for CDs, but it is a product calculator: no nominal-to-effective conversion and no frequency table for a general principal.
- Size.ly and Finnable compound tools: clean single-scenario calculators with the formula stated. Gap: one frequency per run, no effective rate, no schedule beyond a small static table.
- The gap this page fills: one lump sum in, and out comes the interest earned with all five frequencies priced on your exact inputs, the effective annual rate to four decimals, the simple-interest baseline that shows what compounding itself contributed ($2,193.97 on the worked example), and a year-by-year schedule, with the schedule’s 30-year cap and fractional-year note disclosed rather than hidden.
Frequently asked questions
Use A = P × (1 + r/n)nt: principal times one plus the periodic rate, raised to the total number of periods. Subtract the principal to get the interest earned.
Simple interest pays only on the original principal (P × r × t). Compound interest pays on the principal plus all previously earned interest, so it grows faster the longer money stays invested.
Modestly. On $10,000 at 6% for 10 years, daily compounding earns $311.81 more than annual compounding ($18,220.29 against $17,908.48). The rate and the time horizon matter far more.
Years to double ≈ 72 ÷ annual rate %. At 8%, money doubles in about 9 years. It is an estimate, most accurate for rates between 6 and 10%.
The true yearly yield after compounding: EAR = (1 + r/n)n − 1. It lets you compare accounts with different compounding frequencies fairly.
At a positive rate, daily compounding is always slightly better than monthly at the same nominal rate, because interest starts compounding sooner. The gap is small: about 0.015 percentage points of EAR at 6%.
The year-by-year schedule applies your chosen frequency within each year and reports the balance at each year-end, so you can see the growth curve.
Yes, both reduce real returns, and inflation erodes purchasing power. This tool shows the gross math; subtract your tax rate and fees for a net figure.
The schedule lists whole years only and stops at 30. If you enter a fractional time such as 2.5 years, the tool lists years 1 and 2 and still adds the capped-at-30-years note, even though nothing was capped: only the fractional part was trimmed. The final amount always uses your full entry, and below one year there is no schedule at all.
Only the symbol printed in front of the amounts. It does not convert between currencies: €10,000 at 6% for 10 years grows by exactly the same numbers as $10,000, just labelled in euros.
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References
- U.S. Securities and Exchange Commission, Investor.gov. Compound Interest Calculator. Accessed October 22, 2026.
- U.S. Securities and Exchange Commission, Investor.gov. Savings Goal Calculator. Accessed October 22, 2026.
- U.S. Securities and Exchange Commission, Investor.gov. Small Savings Add Up to Big Money. Accessed October 22, 2026.
- OpenStax, Rice University. College Algebra 2e, Section 6.1: Exponential Functions. Accessed October 22, 2026.
- Wolfram MathWorld. Compound Interest. Accessed October 22, 2026.
- U.S. Department of the Treasury, TreasuryDirect. I Bonds. Accessed October 22, 2026.
- U.S. Department of the Treasury, TreasuryDirect. EE Bonds. Accessed October 22, 2026.
- Federal Deposit Insurance Corporation. Simple Strategies for Saving Money on Loans and Credit Cards. Accessed October 22, 2026.
- Financial Industry Regulatory Authority (FINRA). Investing Basics. Accessed October 22, 2026.
- Federal Reserve Bank of St. Louis. How Compound Interest Works and How to Estimate It. Accessed October 22, 2026.