HourlyMath

How to Calculate a Tip in Your Head (and Split the Bill Without Drama)

Updated July 2026 · 4 minute read

Tip math is the most public arithmetic most adults ever do — performed at a table, slightly tired, under mild social observation. The good news: two mental tricks cover every percentage you'll ever need, and one fairness principle settles every group bill. Master these and the end of dinner becomes the easiest part.

The decimal trick (learn one move, get every tip)

Everything builds from 10%, which requires no math at all: $84.00 → $8.40. From there:

• 20% — double it: $16.80. (The standard for decent US table service.)
• 15% — 10% plus half of 10%: $8.40 + $4.20 = $12.60.
• 25% — double 10%, add half of 10%: $16.80 + $4.20 = $21.00. (Excellent service, or you occupied the table for three hours.)
• 18% — 20% minus a little, or 15% plus a little; nobody at the table will audit you. $15 is fine.

Round the bill first ($83.47 → $84 — or $85, since rounding up is the cheapest generosity there is) and the whole performance takes four seconds. The tip calculator handles it when the evening has been long, and splits it in the same motion.

Pre-tax or post-tax? (The eternal question)

The etiquette convention: tipping on the pre-tax subtotal is fully sufficient — the service was on the food, not the tax. In practice, many people tip on the total because it's the number at the bottom of the check. The stakes are smaller than the debates: on a $100 subtotal with 8% tax, 20% either way differs by $1.60. Pick a convention, apply it calmly, and never let the difference hold up a table. (Counter service and its tablet prompts are a matter of personal policy; table service, delivery, bartenders, and anyone hauling your luggage remain solidly in tipping territory in the US.)

Service charges are not tips

The line item that fools everyone: a mandatory service charge or auto-gratuity (common for large parties, increasingly common everywhere) is set by the restaurant, and doesn't always flow to servers the way a tip does. The rules: read the bill before tipping — if 18–20% service is already included, additional tip is genuinely optional (a small extra for great service is kind, not owed). And on large-party bills, check twice: paying a 20% auto-gratuity and then adding your own 20% out of habit is the most expensive reading-comprehension failure in dining.

Splitting: even vs by item

The fairness principle in one line: match the split to the spread of the orders. When everyone ordered similarly, split evenly — total ÷ people, done; a dollar or two of noise is the price of friendship. When orders diverged — one person had soup, another had steak and three cocktails — split by item: each pays their own order plus their proportional share of tax and tip. That proportionality is the step people miss: if your food was 30% of the subtotal, you owe 30% of the tax and tip too, not an even quarter of it. The steak-and-cocktails diner subsidized by even splits is a real phenomenon with a real name in every friend group; item splitting exists so the name doesn't have to be used.

The graceful group-bill playbook

Decide the method before the check lands (a five-second "even split okay?" when ordering settles it). One person pays; others reimburse — cleaner for the restaurant, and payment apps erased the old awkwardness. Compute tip on the whole bill, then divide, rather than collecting individual tips (which mysteriously always under-total). And when in doubt, round up — across a year, the habit costs less than one coffee a month and buys a reputation.