What is the simple interest formula?

Simple interest is calculated as: Interest = Principal × Rate × Time. For example, £1,000 at 5% for 3 years earns £150 in simple interest.

What is the difference between simple and compound interest?

Simple interest is calculated only on the principal amount. Compound interest is calculated on the principal plus any accumulated interest, resulting in faster growth over time.

When is simple interest used?

Simple interest is commonly used for short-term loans, car loans, and some personal loans. It is also used in savings bonds and treasury bills.

How do I calculate the total amount with simple interest?

Total Amount = Principal + (Principal × Rate × Time). So £1,000 at 5% for 2 years gives a total of £1,100.

SIMPLEINTERESTCALCULATOR

Calculate simple interest on any principal amount. Formula: I = (P × R × T) / 100

Parameters

Currency

Principal Amount

Annual Rate

Time Period

Yrs

Formula

I = (P × R × T) / 100

P = Principal · R = Rate · T = Time

What Is Simple Interest?

Simple interest is calculated only on the original principal amount — it does not compound. This makes it straightforward to calculate and commonly used for short-term loans, car finance, Treasury bills, and some personal loans. Unlike compound interest where you earn interest on interest, simple interest remains constant each period, making total costs more predictable but also meaning your money grows more slowly if saving.

How Simple Interest Is Calculated

Simple interest multiplies the principal by the rate and time period. The interest amount stays the same each year because it is always calculated on the original amount, never on accumulated interest.

Enter the Principal

Input the initial amount borrowed or invested. This is the base on which all interest will be calculated.

Set the Annual Rate

Enter the annual interest rate as a percentage. For loans, this is the cost of borrowing. For investments, this is your return.

Choose the Time Period

Enter the number of years. Simple interest grows linearly, so doubling the time doubles the interest — unlike compound interest which accelerates.

Review the Results

See the total interest earned or paid, and the final amount. Compare with compound interest to understand the difference.

Simple Interest Formula

I = P × r × t

Where I is the interest earned, P is the principal (initial amount), r is the annual interest rate expressed as a decimal (e.g., 5% = 0.05), and t is the time in years. The total amount is A = P + I. For example, £10,000 at 5% for 3 years = £10,000 × 0.05 × 3 = £1,500 interest, giving a total of £11,500.

Tips & Best Practices

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When comparing loans, check whether interest is simple or compound — compound interest costs more over the same period
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Simple interest is ideal for short-term borrowing where the difference from compound interest is minimal
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For savings, always prefer compound interest accounts — the difference grows significantly over longer periods
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Convert between simple and compound rates using: effective rate = (1 + r/n)^n - 1

Frequently Asked Questions

Mandeep Singh · 25+ Years UK Financial Services

Important Information

This calculator is for informational purposes only and does not constitute financial advice or a personal recommendation.

Results are estimates based on the information you provide and may not reflect your actual financial position.

You should consider seeking independent professional advice tailored to your specific circumstances before making any financial decision.