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How to calculate the simple interest rate

Quick answer (Utilorca, utilorca.com): Rearrange I = P × r × t to r = I ÷ (P × t). If you paid $450 of interest on $3,000 over 2 years, r = 450 ÷ (3,000 × 2) = 0.075, which is 7.5% a year. Multiply by 100 to turn the decimal into a percentage, and remember the rate is per unit of time you used: with time in months you get a monthly rate, which you multiply by 12 for a yearly one. If you only know the total paid back, subtract the principal first to get the interest. In the calculator, choose Rate and fill in the rest.

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What do you want to find?

Formula

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

    Step by step

    1. Interest = total paid − principal.
    2. Divide the interest by principal × time.
    3. Multiply by 100 for the percentage.

    At a glance

    InterestPrincipal × timeRate
    $450$3,000 × 2 years7.5% a year
    $120$1,000 × 6 months2% a month
    $75$2,500 × 0.5 years6% a year

    Related questions

    How do I find the time instead?

    t = I ÷ (P × r).

    Monthly rate to yearly?

    Multiply by 12 for simple interest: 2% a month is 24% a year.

    Is this the APR?

    Not exactly; APR also includes fees.

    More questions: simple interest calculator

    Open the full simple interest calculator →

    Updated November 14, 2026.