About

Finding the whole number when you only know a percentage and the partial value is a standard problem in both algebra and retail. For instance, if you paid &dollar;120 and know that includes a 20% tax, what was the original price? Or, if 50 students represent 10% of the school, how many students are there in total?

This tool reverses the standard percentage equation. Instead of multiplying by the rate, it divides the part by the decimal form of the percentage. It features three modes: General Math (pure abstract calculation), Sales Tax (backing out tax), and Discount (finding the price before the sale).

Formulas

The fundamental algebraic equation is:

Part = Whole × Percentage100

Rearranging to solve for the Whole:

Whole = Part × 100Percentage

Reference Data

Scenario	Formula	Example
Find Whole	Total = Part% / 100	20 is 10% of 200
Reverse Tax	Price = Total1 + TaxRate	110 w/ 10% tax → 100
Reverse Discount	Orig = SalePrice1 − DiscRate	80 is 20% off → 100

Frequently Asked Questions

Divide the total price paid by (1 + Tax Rate). For example, if you paid $108 and tax is 8% (0.08), calculate 108 / 1.08 = $100.

Divide 50 by 20% (which is 0.20). 50 ÷ 0.20 = 250.

Total = Part / (Percentage / 100).