Calculate 20% Tip in Your Head — Three Shortcuts That Always Work

Twenty percent is the easiest tip to do in your head because the math is one step. Three shortcuts all give the same answer — use whichever feels fastest. On a $48 bill, 20% is $9.60. You can get there in about three seconds without reaching for your phone. Below are the methods, when each one is fastest, and a free free tip calculator for the rare bill where mental math gets messy.

Method 1: Move the Decimal, Then Double

The cleanest approach for most people.

1. Find 10% by moving the decimal point one place to the left. $86.50 becomes $8.65.
2. Double that number. $8.65 × 2 = $17.30.
3. That is your 20% tip.

Works because 20% is just 10% × 2, and 10% is pure decimal movement — no actual arithmetic. Fast on clean numbers, slightly slower on messy ones like $47.83 where you have to double $4.783.

Method 2: Divide the Bill by Five

Faster than the decimal shift on round-number bills because there is no decimal juggling.

1. $100 ÷ 5 = $20
2. $75 ÷ 5 = $15
3. $60 ÷ 5 = $12
4. $40 ÷ 5 = $8

Twenty percent is exactly one-fifth. If your bill ends in a clean 0 or 5, division by 5 is usually the quickest way to the answer. For messy numbers, round the bill up to the nearest $5 first — a $47 bill rounds to $50, divides to $10, close enough.

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Method 3: Double the Tax Line (US Only)

This one is region-specific and fast. If your local sales tax is right around 8–10%, doubling the tax line on the receipt gives you a close approximation of a 20% tip.

• NYC tax (8.875%): double the tax to approximate 17.75% — add a bit for a 20% tip.
• California (varies 7.25–10.75%): works cleanly at 10% — double the tax is exactly 20%.
• Texas (6.25–8.25%): double the tax, add a buck or two.

This is the lazy bartender method — no math required, just read the tax number and double it. Not exact, but always close enough.

Round Up — Nobody Notices Cents

The enemy of fast tip math is decimals. Always round up before you start:

• $87.40 → round up to $90
• $73.85 → round up to $75
• $22.30 → round up to $25

Then apply the trick. 20% of $90 is $18 — three seconds. The extra 50¢ on the actual bill doesn't matter. Your server appreciates the round-up, your dinner partner does not have to witness decimal arithmetic, and nobody audits your tip math.

When to Reach for the Calculator

Three situations where mental math falls apart:

1. Large parties splitting unevenly. Once you are doing "Jake had two beers extra, Sarah is vegetarian so her salad was cheaper," you need a tool.
2. Weird percentages. 22% or 18% for the auto-gratuity test. Not as clean as 20%.
3. Receipts in another currency. Tip math in pesos or euros does not stick in your head the way dollar math does.

Our free tip calculator handles all three in one tap. Type the bill, pick the percentage, set the split. The whole thing runs in your browser — no uploads, no account.

Frequently Asked Questions

What is 20% of $47?

Exactly $9.40. Round up to $10 on the receipt to save the decimal thinking.

Is there a trick for 18% instead of 20%?

Yes — find 20% first using the decimal-and-double method, then subtract 10% of that. 20% of $60 is $12, 10% of $12 is $1.20, so 18% of $60 is about $10.80. Close enough to eyeball.

How do I calculate 20% tip on a $200 dinner in my head?

$200 ÷ 5 = $40. Three seconds. The divide-by-five trick is always fastest on clean bill amounts.

Does rounding up matter if I am tipping 20%?

It smooths the math. $87 × 20% = $17.40. Round the bill up to $90, calculate $18, leave that. The server gets a slightly bigger tip, you skip the decimal work.