📈Simple Interest Calculator — Calculate I=Prt and compare with compound interest

This Simple Interest Calculator computes interest and total amount for both simple and compound interest models so you can compare them directly. Enter principal, annual interest rate, and time period, and the calculator returns interest earned or owed, total amount, and a side-by-side comparison table showing how the two models diverge over time.

Simple interest uses the formula I = P × r × t, where principal stays constant throughout the period. Every year, the same amount of interest accrues on the original principal only. This model is used for short-term loans, car title loans, some consumer bonds, and structured credit products. Because interest does not compound, borrowers pay less total interest than with compound interest at the same nominal rate — which is why many borrowers prefer simple interest loans.

Compound interest uses A = P × (1 + r/n)^(n×t), where earned interest is added back to the principal and then earns interest itself. This is the model used for savings accounts, certificates of deposit, investment accounts, mortgages, and most modern lending. Over short periods, the difference between simple and compound is small. Over long periods — decades of saving or decades of debt — compound interest produces dramatically different totals.

For borrowers, understanding the difference helps evaluate loan offers. A personal loan advertised at simple interest versus a credit card at compound interest with the same nominal rate will cost very different amounts over a year. This calculator makes that comparison instant with a direct side-by-side output.

For savers, compound interest is your ally. A $10,000 investment at 7% for 30 years grows to $76,123 with annual compound interest versus only $31,000 with simple interest. The calculator shows this compounding effect year by year so you can see how the gap widens over time.

This calculator handles daily, monthly, quarterly, and annual compounding frequencies. More frequent compounding means slightly higher effective yield for the same nominal rate. The difference between monthly and daily compounding is small for typical rates, but the calculator shows Effective Annual Rate (EAR) for any compounding frequency so you can compare products on a like-for-like basis.

For students and test-takers, the formula derivation and worked examples help build intuition for interest calculations that appear in standardized tests, personal finance courses, and accounting curricula.

Simple interest and compound interest use fundamentally different base calculations.

Simple Interest Interest = P × r × t Total Amount = P + Interest = P × (1 + r × t)

Where: - P = principal - r = annual rate (decimal form: 5% = 0.05) - t = time in years

Compound Interest A = P × (1 + r/n)^(n × t)

Where: - n = compounding frequency per year Annual: n = 1, Quarterly: n = 4, Monthly: n = 12, Daily: n = 365

Effective Annual Rate (EAR) EAR = (1 + r/n)^n − 1

Comparison example Principal: $5,000 | Rate: 6% | Term: 5 years

Simple interest: I = 5000 × 0.06 × 5 = $1,500 Total = $6,500

Compound interest (monthly, n=12): A = 5000 × (1 + 0.06/12)^(12×5) A = 5000 × (1.005)^60 = 5000 × 1.34885 = $6,744.25 Total interest = $1,744.25

Difference: $244.25 more with compound interest over 5 years at the same rate.