How it works
Adding tax is a multiplication: a net price of 100 at 20% becomes 100 × 1.20 = 120. Removing it is a division, not a subtraction: 120 ÷ 1.20 = 100. Taking 20% off 120 would give 96, which is the most common mistake.
Gross = Net × (1 + rate) · Net = Gross ÷ (1 + rate)
- rate — tax rate as a decimal (20% = 0.20)
The default rate is the standard rate where your currency is used; change it for reduced rates, such as food or books, or for a different state or country.