Compound vs Simple Interest Calculator
How much more compound interest earns.
Compare compound interest against simple interest on the same principal, rate, and term. Enter years to see future values under compound vs simple interest.
What this tool does
This calculator models the earnings difference between two interest calculation methods. Enter your starting amount, annual interest rate, investment timeframe, and how often interest compounds each year. The tool calculates what you'd earn using simple interest—where interest accrues only on your original principal—and compares it to compound interest, where interest earned also generates its own returns. The output shows both final totals, the raw interest difference between them, and the compounding advantage as a percentage gain. Results are most sensitive to longer timeframes and higher compounding frequencies. A typical scenario: comparing a fixed deposit that compounds quarterly against one using simple interest terms. Note that this illustration assumes a constant rate with no deposits or withdrawals, and doesn't account for taxes or inflation.
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Formula Used
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Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
Why the Two Methods Diverge
Simple interest applies the rate to the original principal only. Compound interest applies the rate to principal plus accumulated interest. Over 1 year at 5%, 1,000 earns 50 either way. Over 10 years the simple total is 1,500 (500 interest); compound is 1,629 (629 interest). Over 30 years simple gives 2,500; compound gives 4,322 — 1.7x more.
When Each Applies
Compound interest applies to savings accounts, CDs/fixed deposits, most bonds, ISAs, and investment accounts. Simple interest applies to some personal loans, auto loans, and short-term finance products. Credit cards technically charge simple daily interest but compound if unpaid. Knowing which applies matters for any money-over-time decision.
The Compounding Frequency Effect
Annual compounding on 5% over 10 years gives FV of 1,629. Monthly compounding gives 1,647. Daily compounding gives 1,649. The gap between annual and daily is small at normal rates but grows meaningfully at higher rates or longer periods. Most modern savings products compound monthly or daily.
Run it with sensible defaults
Using principal of 10,000, annual rate of 5, years of 10, compounding per year of 12, the calculation works out to 1,470.85. The defaults are meant as a starting point, not a recommendation.
The levers in this calculation
The inputs — Principal, Annual Rate, Years, and Compounding per Year — do not pull with equal force. The rate and the time horizon usually dominate — compounding means a small change in either reshapes the final figure more than a similar shift in contribution size. Test this by doubling one input at a time.
How the math works
Simple total equals principal plus rate times principal times years. Compound total equals principal times (1 plus rate/compounding) to the power of compounding times years. Advantage is the difference. Results are estimates for illustration purposes only.
How to use this beyond the first run
Re-run the calculation once a year. Life changes — pay rises, new expenses, interest-rate shifts — and the figure that looked right 12 months ago often isn't today. Annual recalibration keeps the plan honest.
What this doesn't capture
The calculation assumes a steady savings rate and a stable interest rate. Real saving journeys include emergencies, windfalls, and rate changes — especially in easy-access products. The figure is a direction of travel, not a guarantee.
Compounding advantage on $10,000 at 5%% over 10 years years is 1,470.09.
Inputs
This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.
Sources & Methodology
Methodology
This calculator computes the difference between compound and simple interest earnings on an initial principal amount. The compound interest total is calculated using the standard compound interest formula, applying the annual rate divided by the compounding frequency, raised to the power of the total number of compounding periods over the full term. The simple interest total multiplies the principal by the annual rate and years to derive interest earned. The advantage shown is the arithmetic difference between these two totals, representing additional earnings from compounding. The model assumes a constant annual rate throughout the term, no deposits or withdrawals, and no fees or taxes. It does not account for inflation, variable rates, or changes in compounding frequency mid-term. Results are estimates for illustration purposes only.
Frequently Asked Questions
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