Tip and Discount Percentage Math

Tips and discounts both use percent-of-a-base math — but the base and the direction differ. A tip adds to what you pay; a discount reduces the price.

Tip formula

tip      = bill × (tip% ÷ 100)
total    = bill + tip
per person ≈ total ÷ people   (if splitting evenly)

Example: $48 bill, 18% tip → tip $8.64 → total $56.64.

Decide whether local custom tips on pre-tax or post-tax amounts — customs vary.

Discount formula

sale price = original × (1 − discount% ÷ 100)
you save   = original − sale price

Example: $80 item, 25% off → pay $60, save $20.

Stacking discounts (careful)

Two sequential 10% discounts ≠ 20% off.

after first 10%:  × 0.90
after second 10%: × 0.90 again → × 0.81 total (19% off)

Coupon-then-sale order can also change the result if each percent applies to a different base (original vs already-reduced). Prefer the register’s stated order over mental addition of percents.

Tip + discount on the same bill

If an item is discounted first, tip on the amount you were actually charged unless local custom says otherwise. Example: $50 meal, 20% off food → $40 food subtotal; 18% tip on $40 → $7.20 (not on the pre-discount $50).

Related tools

• TryCalculatingNow Tip Calculator for tip % and splits
• TryCalculatingNow Discount Calculator for off-price math
• Broader % modes: percentage calculator

Privacy

Bill amounts stay in your browser — no need to type card totals into a random cloud page.

FAQ

Should tip include tax?

Follow local etiquette; calculators let you choose the base.

Is “20% off then extra 10%” the same as 30%?

No — apply sequentially unless the store states a single combined rate.

How do I reverse a tip-included total?

If total includes an 18% tip: bill ≈ total ÷ 1.18.

Can discounts make a price negative?

Not with normal % off under 100%. Check for data entry errors if results look absurd.