How to calculate discounts, tips & taxes
Every calculation this site does, explained step by step in one spot. Learn the formulas behind sale prices, bill splitting, and local sales tax — then jump straight to the calculator you need.
💰 Discounts
How to calculate a discount
The formula
Sale Price = Original Price − (Original Price × Discount % ÷ 100)
- 1Write down the original price and the discount percentage.
- 2Convert the percentage to a decimal by dividing by 100 (e.g. 25% → 0.25).
- 3Multiply the original price by that decimal to find your savings.
- 4Subtract the savings from the original price to get the sale price.
Worked example
A $60 shirt at 25% off: $60 × 0.25 = $15 saved, so the sale price is $60 − $15 = $45.
🏷️ Reverse discount
How to find the percentage off from a price
The formula
Discount % = ((Original Price − Paid Price) ÷ Original Price) × 100
- 1Subtract the price you paid from the original price to find your savings.
- 2Divide those savings by the original price.
- 3Multiply the result by 100 to get the percentage off.
Worked example
An $80 item you paid $60 for: ($80 − $60) ÷ $80 × 100 = 25% off.
🧾 Tips
How to calculate a tip
The formula
Tip = Subtotal × (Tip % ÷ 100) · Total = Subtotal + Tip
- 1Use the bill subtotal — the amount before tax.
- 2Convert your tip percentage to a decimal (e.g. 18% → 0.18).
- 3Multiply the subtotal by that decimal to find the tip amount.
- 4Add the tip to the subtotal for the grand total.
- 5To split, divide the grand total by the number of people.
Worked example
An $80 bill with an 18% tip: $80 × 0.18 = $14.40 tip, $94.40 total. Split 4 ways: $23.60 each.
📍 Tax + Discount
How to calculate tax on a discounted price
The formula
Tax = Sale Price × (Tax Rate ÷ 100) · Final = Sale Price + Tax
- 1Apply the discount first to get the sale price (see step 1).
- 2Find your local combined sales tax rate as a decimal.
- 3Multiply the sale price by that decimal to find the sales tax.
- 4Add the tax to the sale price for the true final total.
Worked example
A $100 item at 30% off with 8% sales tax: $100 − $30 = $70 sale price. Tax = $70 × 0.08 = $5.60. Final = $75.60.
🧩 Putting it all together
A real shopping trip often uses all three calculations at once. Here is the full chain: apply a discount to get the sale price, then add local sales tax to that sale price for your true total. If you are dining out, calculate the tip on the subtotal before tax, then split the grand total between your group.
1. Discount
Lower the sticker price by the discount percentage to find what the item actually costs before tax.
2. Tax
Multiply the discounted price by your local sales tax rate, then add it on — tax always applies to the sale price, not the original.
3. Tip (dining)
For restaurants, tip on the pre-tax subtotal, then divide the grand total by the number of diners to split evenly.
Full worked example
A $120 jacket at 40% off in a state with 8% sales tax: discount saves $48 → sale price $72. Tax = $72 × 0.08 = $5.76. Final total = $77.76. At a restaurant, an $80 subtotal with an 18% tip and 8% tax: tip $14.40, tax $6.40, grand total $100.80 — split 4 ways is $25.20 each.
📌 Quick reference: the formulas
Bookmark this cheat sheet of every formula covered above.
| What you want | Formula |
|---|---|
| Sale price | Original − (Original × Discount% ÷ 100) |
| Savings | Original × Discount% ÷ 100 |
| Percentage off | ((Original − Paid) ÷ Original) × 100 |
| Tip amount | Subtotal × Tip% ÷ 100 |
| Per person | (Subtotal + Tip) ÷ Number of people |
| Sales tax | Sale Price × Tax Rate% ÷ 100 |
| Final total | Sale Price + Sales Tax |