Percentage Calculator

Every kind of percentage question in one place — percent of a number, what percent, increase and decrease, the whole from a part, marks to percentage and conversions — each with a visual bar and full working.

Class 5–10 Mathematics 7 calculators Marks & CBSE grade

Percent means per hundred. To find X% of Y, multiply Y by X ÷ 100: 15% of 640 = 0.15 × 640 = 96. To turn a part into a percentage, divide by the whole and multiply by 100, so 432 marks out of 500 is 432 ÷ 500 × 100 = 86.4%. For a change, always divide by the original value.

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Step-by-step working

    How it works

    Percent simply means per hundred

    Pick the type of question, type your numbers and get the answer with a picture and the exact working you would write in your notebook.

    Choose the question type

    Seven calculators cover almost every percentage problem from Class 5 to Class 10.

    Fill in the sentence

    The inputs read like the question — “What is 15% of 640?” — so you always know what goes where.

    Read the bar

    The visual bar shows the part against the whole, or the old value against the new.

    Copy the steps

    Each step uses your numbers, with a quick mental-maths shortcut where one exists.

    Percent of a number

    X% of Y = (X ÷ 100) × Y

    25% of 80 = 0.25 × 80 = 20. Tip: X% of Y = Y% of X, so 8% of 50 = 50% of 8 = 4.

    What percent?

    % = (part ÷ whole) × 100

    18 out of 24 → 18 ÷ 24 × 100 = 75%. The same rule turns marks into a percentage.

    Increase & decrease

    % change = (new − old) ÷ old × 100

    Always divide by the original value. To increase by r%, multiply by (1 + r/100); to decrease, multiply by (1 − r/100).

    Fraction ↔ decimal ↔ percent

    Fraction → decimal: divide top by bottom. Decimal → percent: multiply by 100. Percent → fraction: write over 100 and simplify: 45% = 45/100 = 9/20.

    Watch out: a 20% rise followed by a 20% fall does not bring you back to the start — 100 → 120 → 96. The second change is worked out on the new value.
    Questions & answers

    Percentage Calculator — your questions

    How do I calculate the percentage of marks?

    Divide the marks obtained by the maximum marks and multiply by 100. For 432 out of 500, that is 432 ÷ 500 × 100 = 86.4%. For several subjects, add up all the marks obtained and all the maximum marks first, then apply the same formula — do not average the individual subject percentages unless every subject has the same maximum.

    What is the formula for percentage increase and decrease?

    Percentage change = (new value − old value) ÷ old value × 100, and a negative result means a decrease. Going from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase. To apply a change, multiply by (1 + r/100) to increase and (1 − r/100) to decrease. Always divide by the original value, not the new one.

    How do I find the whole when I know a percentage of it?

    Divide the part by the percentage and multiply by 100. If 20% of a number is 50, the number is 50 ÷ 20 × 100 = 250. Written as an equation, 0.20 × n = 50, so n = 50 ÷ 0.20 = 250. Checking is easy: 20% of 250 is indeed 50.

    What grade is 86% on the CBSE school scale?

    On the CBSE school grading scale used for scholastic subjects, 86% falls in the 81–90 band, which is grade A2 with 9 grade points. The bands are 91–100 A1, 81–90 A2, 71–80 B1, 61–70 B2, 51–60 C1, 41–50 C2 and 33–40 D, with 33% as the pass mark and anything below that graded E.

    Does a 20% rise followed by a 20% fall bring you back to the start?

    No. Start at 100, add 20% to reach 120, then take 20% off 120, which removes 24 and leaves 96 — a net 4% loss. The second percentage is worked out on the new, larger value, not the original. Two successive changes of a% and b% combine to a + b + ab/100 overall.

    How do I convert a percentage to a fraction or decimal?

    To get a fraction, write the percentage over 100 and simplify: 45% = 45/100 = 9/20. To get a decimal, divide by 100, so 45% = 0.45. Going the other way, multiply a decimal by 100 to get the percentage. Useful ones to memorise are 1/8 = 12.5%, 1/4 = 25%, 1/3 = 33⅓% and 3/4 = 75%.

    What is a quick way to find a percentage mentally?

    Use the swap rule: X% of Y is always equal to Y% of X, so 8% of 50 is the same as 50% of 8 = 4. Build the rest from 10%, which is just moving the decimal point one place: 10% of 640 is 64, so 5% is 32 and 15% is 64 + 32 = 96.