Calculate interest earned or owed on any principal amount — switch between simple and compound interest.
Enter Interest Details
Choose simple or compound interest, fill in the details, and click Calculate.
An interest calculator works out how much interest a principal amount earns or costs over time, letting you switch between simple interest and compound interest and see both side by side as a built-in SI vs CI calculator. It applies to either side of a transaction — interest on savings you're depositing or investing, or interest on a loan you're borrowing — across 10 currencies, so it suits savers comparing account types, borrowers checking loan terms, and anyone who just wants to see the practical difference between the two interest methods.
Enter a principal amount, an annual interest rate, and a time period in years and months. In Simple Interest mode, the calculator applies SI = P × R × T, meaning interest is calculated only on the original principal every period and grows in a straight line. In Compound Interest mode, it applies A = P × (1 + r/n)^(n×t), where n is your chosen compounding frequency (annually, semi-annually, quarterly, monthly, or daily) — here, interest earned in earlier periods is added to the balance and itself starts earning interest, so the total grows faster the longer it runs and the more frequently it compounds. The results panel always shows both totals together along with a year-wise growth chart, so this doubles as an SI vs CI calculator that shows exactly how far ahead compound interest pulls over the same term.
Savers comparing a fixed deposit against a compounding savings account, borrowers checking whether a short-term loan uses simple or compound interest, students learning the mechanics of interest math, and anyone who wants a quick side-by-side SI vs CI comparison before choosing a financial product.
Whether an account or loan uses simple or compound interest — and how often it compounds — has a real effect on the final numbers, especially over longer terms. As a saver or investor, compound interest works in your favor, and more frequent compounding means slightly more return for the same nominal rate, so it pays to know how your bank calculates interest on savings. As a borrower, simple interest usually costs less over time than compound interest at the same rate, which is why understanding which method applies to the interest on your loan matters before you sign anything.
Choose the interest type that matches your loan, deposit, or investment
Calculated only on the original principal. Grows linearly — the same amount of interest accrues every year. Common in some short-term loans and promissory notes.
Calculated on the principal plus previously accumulated interest. Grows exponentially. Used by most savings accounts, term deposits, and long-term loans.
As a borrower, simple interest usually costs less over time. As a saver or investor, compound interest earns more. Check your loan or account terms to see which applies.
From principal to results in under a minute
Pick the interest type that matches your savings account, deposit, or loan agreement — or leave it on the default and use the built-in comparison to see both anyway.
Input the amount being deposited, invested, or borrowed, and select from 10 supported currencies — every result updates instantly when you switch currency.
Use the nominal annual rate quoted by your bank, lender, or investment provider — not an already-compounded APY figure.
Enter the duration in years and months, then — for Compound Interest — choose how often interest compounds: annually, semi-annually, quarterly, monthly, or daily.
Review the interest earned, total amount, a side-by-side Simple vs Compound comparison, and a year-wise growth chart, then download a plain-text summary if you need it.
A realistic 5-year deposit, calculated both ways
Suppose you deposit a $10,000 principal at a 6% annual interest rate for 5 years. Compare what you'd earn under simple interest versus compound interest with monthly compounding.
Explanation: Both scenarios start with the identical $10,000 principal and 6% nominal rate — the only difference is whether interest is calculated once on the original principal (simple) or recalculated on a growing balance twelve times a year (compound). Notice the gap between the two totals widens the longer the money stays invested, which is why compounding matters more for long-term savings goals than short ones.
Frequency comparison: If the same $10,000 at 6% for 5 years compounded annually instead of monthly, A = 10,000 × (1.06)⁵ ≈ $13,382.26 — about $106 less than monthly compounding, illustrating how compounding frequency alone shifts the result even when the nominal rate and term don't change.
What the gap between your Simple and Compound totals actually tells you
A quick way to gauge how much compounding is worth in your scenario is the compounding advantage — the compound interest total minus the simple interest total, expressed as a percentage of the simple interest total.
| Compounding Advantage | General Read | Typical Context |
|---|---|---|
| Under 10% | Small advantage | Short terms (1–3 years) or lower rates |
| 10% – 30% | Moderate advantage | Mid-term deposits (5–10 years) at typical savings rates |
| Over 30% | Substantial advantage | Long terms (15+ years), higher rates, or frequent compounding |
For savers and investors: a larger compounding advantage means more of your final balance came from the interest-on-interest effect rather than the passage of time alone — a strong argument for choosing compounding accounts over simple-interest ones whenever the nominal rates are comparable.
For borrowers: the same math works against you — a loan that compounds costs meaningfully more than an equivalent simple-interest loan at the same nominal rate, especially over longer terms. Always confirm which method your loan agreement actually uses.
Risk considerations: this calculator assumes a fixed rate for the entire term with no missed deposits, withdrawals, or rate changes. Real accounts and loans can have variable rates, fees, taxes on interest income, or penalties for early withdrawal that this simple projection doesn't capture.
This tool provides general financial estimates for educational purposes only and does not constitute personalized financial or investment advice. Past performance isn't a guarantee of future results — confirm actual rates and terms with your bank, lender, or a licensed financial advisor before making a decision.
Where this interest calculator earns its keep
Compare a compounding savings account against a simple-interest alternative at the same nominal rate.
Estimate maturity value on a term deposit before locking in funds for a fixed period.
Cross-check a lender's quoted interest figure on a short-term or promissory-note loan.
Work out fair interest on an informal lending arrangement between individuals.
See exactly how much extra compounding adds over the same principal, rate, and term.
Demonstrate the practical difference between linear and exponential interest growth.
Model interest scenarios across 10 currencies for relocation or international accounts.
See how monthly vs. annual vs. daily compounding changes the same nominal rate's real return.
Get an instant estimate before running numbers through a bank's official calculator.
What this interest calculator does well, and where it can't replace professional advice
Quick-reference comparison of the two interest methods this calculator supports
| Feature | Simple Interest | Compound Interest |
|---|---|---|
| Growth pattern | Linear (straight line) | Exponential (curves upward) |
| Calculated on | Original principal only | Principal + accumulated interest |
| Typical use | Short-term loans, promissory notes | Savings accounts, term deposits, long-term loans |
| Total for saver/borrower | Lower total interest | Higher total interest (same rate) |
| Formula inputs needed | Principal, rate, time | Principal, rate, time, compounding frequency |
Common questions about calculating interest
Official guidance to complement this calculator — not a substitute for licensed financial advice
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