Math Guide

Percentage Calculator Guide: All the Formulas You Need

Percentages appear everywhere — discounts, tax, marks, interest, growth rates. Here are all the essential formulas with clear examples.

The 4 Core Percentage Formulas

X% of Y

Result = Y × (X ÷ 100)

15% of 200 = 200 × 0.15 = 30

X is what % of Y

% = (X ÷ Y) × 100

45 is what % of 180? = (45÷180) × 100 = 25%

Percentage increase

% = [(New − Old) ÷ Old] × 100

₹400 → ₹500: [(500−400)÷400] × 100 = 25%

Percentage decrease

% = [(Old − New) ÷ Old] × 100

₹500 → ₹400: [(500−400)÷500] × 100 = 20%

Common Uses of Percentages

Exam scores

You got 72 out of 90 marks → (72÷90)×100 = 80%

Sales discount

₹1,500 at 20% off → Save ₹300, pay ₹1,200

Inflation rate

Price rose from ₹50 to ₹57 → 14% inflation

Interest rate

₹10,000 at 7% p.a. → ₹700 interest per year

Tip calculation

₹850 bill, 15% tip → ₹127.50 tip

Body fat %

Fat mass ÷ total body weight × 100

Frequently Asked Questions

How do I calculate what percentage X is of Y?

Percentage = (X ÷ Y) × 100. For example, what percentage is 45 of 200? = (45 ÷ 200) × 100 = 22.5%.

How do I find X% of a number Y?

Result = Y × (X ÷ 100). What is 15% of ₹8,000? = 8,000 × 0.15 = ₹1,200.

How do I calculate percentage increase?

Percentage Increase = [(New Value − Old Value) ÷ Old Value] × 100. Price went from ₹500 to ₹650: Increase = [(650−500)÷500] × 100 = 30%.

How do I calculate percentage decrease?

Percentage Decrease = [(Old Value − New Value) ÷ Old Value] × 100. Price dropped from ₹1,000 to ₹750: Decrease = [(1,000−750)÷1,000] × 100 = 25%.

What is the percentage difference between two numbers?

Percentage Difference = |Value1 − Value2| ÷ [(Value1 + Value2) ÷ 2] × 100. This treats both numbers equally, unlike percentage change which assumes a direction.

Related Calculators

Tax percentage on goods

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