How to calculate a tip without a calculator

Every tip percentage you will ever need is built from one move: find 10%, then scale. Once that's reflex, a restaurant bill takes five seconds of head math — and when the table is six people and three shared starters deep, the tip calculator does the same arithmetic with a split button. Here's the mental version first.

The 10% trick

Ten percent of anything is the number with the decimal point moved one place left: 10% of $84.60 is $8.46. Every standard tip is a simple assembly of that piece:

• 15% = 10% + half of it. ($8.46 + $4.23 ≈ $12.70)
• 18% = 20% minus a tenth of the 20%. Easier in practice: double the 10% ($16.92), knock a bit less than a tenth off — ≈ $15.20.
• 20% = 10% doubled. ($16.92)
• 25% = 10% doubled, plus half of 10%. ($16.92 + $4.23 ≈ $21.15)

Two shortcuts make it even faster. Round the bill first — $84.60 is $85, and nobody tips to the cent. And for 20%, the most common tip in the US, the whole procedure is: round, double, shift the decimal. $85 → 170 → $17.00.

Standard amounts by situation

US conventions, since that's where tipping is closest to mandatory:

• Restaurant table service: 15–20% is standard; 20%+ for great service. Below 15% reads as a complaint.
• Bars: $1–2 per drink, or 15–20% on a tab.
• Delivery: 10–15% with a sensible minimum — short cheap orders still cost the driver the same trip, so $3–5 floors are common courtesy.
• Taxis and rideshares: 10–15%, or round up generously.
• Hair and personal services: 15–20%.
• Counter service and takeaway: genuinely optional — the tip jar and the tablet's suggested 25% are asking, not owed.

Pre-tax or post-tax?

Etiquette formally says the pre-tax subtotal; in practice most people tip on the total because it's the number at the bottom of the bill. The difference is small — on a $85 bill with 9% tax, 20% pre- versus post-tax is about $1.50 — so this is a question with a correct answer and no stakes. If the service was good, tipping on the total is the generous default; if you like precision, the subtotal is on the receipt.

Splitting the bill

The clean method: add the tip to the total first, then divide by people — everyone's share includes their tip and nobody does percentage arithmetic individually. An $84.60 bill, 20% tip, four people: $84.60 + $16.92 = $101.52, so $25.38 each. Rounding up to tidy numbers per person ($26) quietly absorbs the awkward cents and slightly pads the tip, which no server has ever objected to. The calculator does the whole thing — tip, total, per-person — as you type, which matters mostly at the end of a long dinner when nobody's arithmetic is at its best.

Tipping around the world

The US habit does not travel. A quick field guide:

• USA & Canada: 15–20% expected at table service; servers' wages are built around it.
• UK & Ireland: 10–12.5% for table service, often added as a "service charge" — check the bill before doubling it. No tipping at pubs.
• Western Europe: service is typically included by law or custom; rounding up or leaving 5–10% for good service is appreciated, not required.
• Japan, South Korea, China: no tipping — it can cause genuine confusion or polite refusal. Exceptional service is thanked in words.
• Southeast Asia, Middle East, Latin America: varies widely; 10% is a safe ceiling where tipping exists at all, and small change is often the norm.
• Australia & New Zealand: not expected; reserved for genuinely exceptional service.

The one universal rule: when a service charge is already printed on the bill, the tip question has been answered for you. Everywhere else, the 10% trick has you covered in any currency — it's just a decimal point, and the same percentage arithmetic you use everywhere else.