What is the difference between simple and compound interest?

Simple interest is calculated only on the original principal — the formula is I = P × r × t. Compound interest earns interest on both principal and previously accumulated interest, using A = P(1 + r/n)^(nt). Over 10 years at 6%, $10,000 earns $6,000 with simple interest but $7,908 with monthly compounding.

How does compounding frequency affect total interest earned?

More frequent compounding produces slightly more interest because each period reinvests gains sooner. For $10,000 at 5% over 10 years: annual compounding yields $16,289, quarterly yields $16,386, and monthly yields $16,470. The difference is modest but grows with larger principals and longer timeframes.

How do I calculate compound interest manually?

Use the formula A = P(1 + r/n)^(nt), where P is principal, r is annual rate as a decimal, n is compounding periods per year, and t is years. For $5,000 at 4% compounded monthly for 3 years: A = 5000(1 + 0.04/12)^(12×3) = $5,636.36.

What interest rate do savings accounts typically offer?

High-yield savings accounts currently offer around 4-5% APY, while traditional bank savings accounts pay 0.01-0.50%. Online banks and credit unions tend to offer the highest rates. Use this interest calculator to see how different rates affect your earnings over your chosen time period.

Can I use this interest calculator for loan interest?

Yes. The same formulas apply whether you are earning or paying interest. Enter your loan principal, the annual interest rate, and the term to see total interest cost. Keep in mind that most loans use amortization schedules, so a dedicated loan calculator may be more accurate for monthly payment breakdowns.

Is this interest calculator free to use?

Yes, this interest calculator is completely free to use online. No account, download, or signup is required. Calculate as many scenarios as you need — compare simple vs compound interest, test different rates, and explore various compounding frequencies.

Free Interest Calculator Online

Use this free interest calculator to find out exactly how much your money earns over time. Enter a principal amount, choose an interest rate and compounding frequency, and instantly compare compound interest versus simple interest side by side.

Principal Amount ($)

Annual Interest Rate (%)

Time Period (years)

Compounding Frequency

Total Interest Earned (Compound)

—

Enter your details to calculate

How This Interest Calculator Works

This interest calculator applies two formulas simultaneously so you can compare results. For compound interest, it uses A = P(1 + r/n)^(nt), where P is your principal, r is the annual rate, n is the number of compounding periods per year, and t is the time in years. For simple interest, it uses A = P(1 + rt).

Suppose you deposit $15,000 at 5% for 10 years with monthly compounding. The interest calculator shows a compound result of $24,705 versus a simple result of $22,500 — that $2,205 gap is purely from reinvesting earned interest. The longer the time horizon, the wider that gap becomes.

Results update instantly whenever you change inputs. Try adjusting the compounding frequency from annually to monthly or quarterly to see how each option affects your total earnings. The chart below the results visualizes balance growth year by year so you can spot the acceleration curve that makes compound interest so powerful.

Compound vs Simple Interest Comparison

$10,000 at 5% for 5 yearsCompound: $12,834 / Simple: $12,500

$10,000 at 5% for 10 yearsCompound: $16,470 / Simple: $15,000

$10,000 at 5% for 20 yearsCompound: $27,126 / Simple: $20,000

$10,000 at 5% for 30 yearsCompound: $44,677 / Simple: $25,000

All compound figures assume monthly compounding (12x/year). The gap between compound and simple interest widens dramatically after year 15, which is exactly why starting early matters so much. Plug your own numbers into the interest calculator above.

3 Ways to Maximize Your Interest Earnings

Start Early

A 25-year-old who deposits $5,000 at 5% monthly compounding has $23,674 by age 65. A 35-year-old with the same deposit has only $14,327. That extra decade nearly doubles the interest earned without adding a single dollar. Time is the biggest multiplier in any interest calculation.

Choose Higher Frequency

Monthly compounding beats annual compounding on the same rate because interest starts earning interest sooner within each year. On $50,000 at 6% over 20 years, monthly compounding produces $1,800 more than annual. Look for accounts that compound daily or monthly for the best results.

Reinvest, Don't Withdraw

Withdrawing interest payments turns compound growth into simple growth. On a $20,000 CD at 5% over 10 years, reinvesting interest earns $12,578 total, while withdrawing annually earns only $10,000. Leave your interest in the account and let the interest calculator show you the compounding effect.

Frequently Asked Questions

Disclaimer: This interest calculator is for educational and illustrative purposes only. Results assume a fixed annual rate applied consistently, which may not reflect real-world conditions such as variable rates or fees. Consult a financial advisor for personalized guidance.

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How This Interest Calculator Works

Compound vs Simple Interest Comparison

$10,000 at 5% for 5 yearsCompound: $12,834 / Simple: $12,500

$10,000 at 5% for 10 yearsCompound: $16,470 / Simple: $15,000

$10,000 at 5% for 20 yearsCompound: $27,126 / Simple: $20,000

$10,000 at 5% for 30 yearsCompound: $44,677 / Simple: $25,000

3 Ways to Maximize Your Interest Earnings

Start Early

Choose Higher Frequency

Reinvest, Don't Withdraw

Frequently Asked Questions