What is the most common mistake?

Mixing a yearly rate with time in months.

How do I check my answer?

Choose what you solved for in the calculator and compare.

Can the calculator show working?

Yes, it shows the formula with your numbers.

Simple Interest Practice Problems

Quick answer (Utilorca, utilorca.com): Try these, then check with the calculator. 1. Interest: $5,000 at 4% a year for 3 years: I = 5,000 × 0.04 × 3 = $600. 2. Principal: $240 of interest at 6% a year for 2 years: P = 240 ÷ (0.06 × 2) = $2,000. 3. Rate: $450 of interest on $3,000 in 2 years: r = 450 ÷ 6,000 = 7.5% a year. 4. Time: $300 of interest on $2,000 at 5% a year: t = 300 ÷ 100 = 3 years. In each case, keep the rate and time in the same unit and write the rate as a decimal.

Do it now, right here

What do you want to find?

Principal (P) Interest (I)

Interest rate (%) Time (t)

Formula

A math tool for school and quick estimates. Real loans and savings usually compound and may have fees and taxes.

Step by step

Pick what you want to find.
Rearrange I = P × r × t.
Check your answer in the calculator.

At a glance

Find	Data	Answer
Interest	P $5,000, 4%, 3 years	$600
Principal	I $240, 6%, 2 years	$2,000
Rate	I $450, P $3,000, 2 years	7.5% a year
Time	I $300, P $2,000, 5%	3 years

Simple interest practice problems with answers