Guide
Percentage, Tip & Tax — Everyday Percent Math
Percent math shows up on receipts, sales tags, and tip jars. This guide ties together percentage of a number, restaurant tips, and sales tax / GST / VAT so you can check a total before you pay.
Updated September 15, 2026
Percentage of a number
“What is P% of N?” means N × P / 100. “N is what percent of M?” means (N / M) × 100. Percent change is (new − old) / old × 100.
Use the Percentage Calculator when you need any of those identities without mental arithmetic.
Tips and bill split
Tip = bill × tip% / 100. Total = bill + tip. Per-person share divides by headcount — decide whether tip is on pre-tax or post-tax as your group prefers.
Customs vary by country and service type; the calculator does the arithmetic, not the etiquette.
Tax, GST, and VAT
Tax-exclusive: taxed amount = price × (1 + rate). Tax-inclusive: net = gross / (1 + rate). GST/VAT tools switch between add-tax and remove-tax modes so invoices stay clear.
Rates and rules differ by place and product — educational estimates only.
Common mistakes
Adding tax and tip in the wrong order when your group agreed on a specific base.
Treating a tax-inclusive price as exclusive (or the reverse).
Stacking percentage discounts incorrectly (20% + 10% off is not always 30% off).
Worked examples
Tip: $80 bill at 18% → tip $14.40, total $94.40; with 4 people ≈ $23.60 each.
VAT: $100 exclusive at 20% → $120 gross. $120 inclusive at 20% → $100 net.
Replay these in the Tip, Percentage, and GST / VAT calculators.