How to Calculate a Tip Without a Calculator

You are sitting at a restaurant. The check arrives. You glance at the total and suddenly your brain goes blank. How much is 18% of $73.40? You reach for your phone, but it feels awkward fumbling with a calculator while everyone else is putting on their coats. Sound familiar?

The good news is that calculating a tip in your head is much easier than you think. You do not need to be a math whiz. With a handful of simple techniques, you can figure out the right tip for any bill in seconds, no phone required. These methods work for 10%, 15%, 18%, 20%, and 25% tips, covering every standard tipping percentage you will ever need.

Of course, if you prefer the easy route, our free tip calculator handles everything instantly. But for those moments when you want to do it yourself, here is your complete guide to tip mental math.

Method 1: The 10% Foundation

This is the single most important trick to learn, because every other method builds on it. Calculating 10% of any number is the easiest math you will ever do: just move the decimal point one place to the left.

• 10% of $50.00 = $5.00
• 10% of $73.40 = $7.34
• 10% of $124.80 = $12.48
• 10% of $8.50 = $0.85

That is it. No multiplication, no division, just slide the decimal. Once you have 10%, you can build any common tip percentage from it using simple addition or doubling.

Getting to 15%

Fifteen percent is just 10% plus half of 10%. Here is how it works in practice:

Example: $60.00 bill

1. 10% of $60 = $6.00
2. Half of $6.00 = $3.00
3. $6.00 + $3.00 = $9.00 tip (15%)

Example: $84.00 bill

1. 10% of $84 = $8.40
2. Half of $8.40 = $4.20
3. $8.40 + $4.20 = $12.60 tip (15%)

The halving step is the only part that requires any thought, and even then, halving a single-digit or low double-digit number is straightforward. If the half is not a clean number, just round to the nearest quarter or dime. Nobody expects your tip to be precise to the penny.

Getting to 20%

Twenty percent is even simpler: just double 10%. This is why 20% is the easiest tip percentage to calculate mentally, and one reason it has become the default for many diners.

Example: $55.00 bill

1. 10% of $55 = $5.50
2. Double $5.50 = $11.00 tip (20%)

Example: $93.00 bill

1. 10% of $93 = $9.30
2. Double $9.30 = $18.60 tip (20%)

Getting to 25%

For exceptional service, 25% is a generous tip. Calculate it as 20% plus half of 10%, or equivalently, double 10% and then add another half of 10%.

Example: $80.00 bill

1. 10% of $80 = $8.00
2. 20% = $8.00 x 2 = $16.00
3. Half of 10% = $4.00
4. $16.00 + $4.00 = $20.00 tip (25%)

Method 2: The Double-Tax Method

This is a popular shortcut that works particularly well in the United States because sales tax is printed right on your receipt. The idea is simple: if your local sales tax is around 8-10%, doubling the tax amount gives you a tip that is roughly 16-20%.

How it works:

1. Look at the tax amount on your receipt
2. Double it
3. That is approximately your tip

Example: Bill is $75.00, tax is $6.56 (8.75% sales tax)

1. Tax = $6.56
2. Double the tax = $6.56 x 2 = $13.12 (approximately 17.5%)

The double-tax method is not perfectly precise, but it gets you in the right ballpark without any real calculation. The accuracy depends on your local tax rate:

Local Sales Tax	Double Tax Equals
7%	~14% tip
8%	~16% tip
8.75%	~17.5% tip
9%	~18% tip
10%	~20% tip

If your local sales tax is around 9%, doubling the tax gives you almost exactly 18%, which is a solid, standard tip. If your tax rate is lower (like 7%), doubling the tax gets you to about 14%, so you might want to add a couple extra dollars to reach 18-20%.

Method 3: The Round-and-Calculate Approach

Mental math is hardest when you are dealing with awkward numbers. A bill of $67.43 is much harder to work with than $70. The solution? Round first, then calculate. You will be off by a few cents at most, and since you are rounding up, you will err on the side of generosity.

Example: $67.43 bill, 20% tip

1. Round $67.43 up to $70
2. 10% of $70 = $7.00
3. 20% = $7.00 x 2 = $14.00

The actual 20% of $67.43 is $13.49, so by rounding up you tipped about 50 cents more. That is hardly noticeable on your end but still fair and generous.

Example: $112.37 bill, 18% tip

1. Round $112.37 up to $115
2. 10% of $115 = $11.50
3. To get to roughly 18%, you need about 10% + 10% minus a little: $11.50 + $11.50 = $23 for 20%, so 18% is slightly less
4. Shortcut: 20% minus about 10% of the 10% figure: $23 - $2.30 = $20.70, round to $21

This approach works because our brains handle round numbers much more efficiently. By removing the mental friction of odd digits, you free up your brainpower for the actual percentage calculation.

Method 4: The Per-Dollar Quick Reference

If you eat out frequently and your bills tend to fall in similar ranges, it helps to memorize a few key reference points. Think of these as mental bookmarks.

Bill Amount	15% Tip	18% Tip	20% Tip
$20	$3.00	$3.60	$4.00
$30	$4.50	$5.40	$6.00
$40	$6.00	$7.20	$8.00
$50	$7.50	$9.00	$10.00
$75	$11.25	$13.50	$15.00
$100	$15.00	$18.00	$20.00
$150	$22.50	$27.00	$30.00
$200	$30.00	$36.00	$40.00

You do not need to memorize the entire table. Just remember the $50 and $100 rows. Since $50 is half of $100, you can quickly interpolate. A $75 bill? That is halfway between $50 and $100, so the 20% tip is halfway between $10 and $20, which is $15.

Method 5: The Splitting Shortcut

When you are splitting a bill with friends, the math gets messier. But there is a trick: calculate the total tip first (using any method above), then divide the tip by the number of people. Dividing a tip amount is usually easier than dividing an entire bill and then calculating individual tips.

Example: $120 bill, 4 people, 20% tip

1. 20% of $120 = $24 total tip
2. $24 divided by 4 = $6 tip per person
3. $120 + $24 = $144 total, divided by 4 = $36 per person

Example: $90 bill, 3 people, 18% tip

1. 10% of $90 = $9, so 20% = $18
2. 18% is slightly less, roughly $16
3. $16 divided by 3 is about $5.33, so round to $5.50 per person

When splitting among friends, precision matters even less. Round up to a clean number that everyone can easily pay. Your server will not mind receiving an extra dollar, and it saves your group the headache of exchanging coins.

Common Scenarios with Worked Examples

Let us walk through some real-world situations to practice these techniques.

Scenario 1: Quick lunch, $18.50 bill

You want to leave 20%. Round $18.50 to $20. Ten percent of $20 is $2. Double it for 20%: $4. Your tip is $4, making the total $22.50. Quick and easy.

Scenario 2: Dinner for two, $87.30 bill

You want to leave 18%. Round to $90. Ten percent of $90 is $9. For 18%, you need about 10% + 8%. Since 8% is roughly 80% of the 10% figure: $9 x 0.8 = $7.20. Total tip: $9 + $7.20 = $16.20. Round to $16 or $17. Alternatively, just calculate 20% ($18) and leave that, since the difference is small and 20% is simpler.

Scenario 3: Group dinner, $235 bill split 5 ways

You want to leave 20%. Ten percent of $235 is $23.50, so 20% is $47. Total becomes $282. Divided by 5: $282 / 5 = $56.40, round to $57 per person. If everyone pays $57, the server gets a $50 tip on a $235 bill, which is about 21%. Close enough and generous.

Scenario 4: Coffee shop, $5.75 bill

For small bills, percentage math is almost unnecessary. A dollar tip on a $5.75 coffee is about 17%, which is perfectly appropriate. For counter service, $1 is a standard tip regardless of the exact percentage. If you want to be generous, leave $2.

Scenario 5: Delivery order, $32.50

Round to $33. Ten percent is $3.30, so 20% is $6.60. Round to $7. For delivery, this is solid. If the weather was bad or the driver had to climb stairs, leave $8 or $9. The minimum for delivery should be $4-5 regardless of the bill, so on a $32 order, $7 is fair.

The 18% Trick: A Special Shortcut

Eighteen percent is one of the most common tip amounts, but it is an awkward number to calculate mentally. Here is a specific trick for 18%:

1. Calculate 10% (move the decimal)
2. Calculate 10% again (same number)
3. Subtract 20% of that 10% figure from the second 10%
4. Add the results

Too complicated? Here is an easier way to think about it: 18% is 20% minus a little bit. Calculate 20% (which is easy: double 10%), then subtract about 10% of that 20% figure.

Example: $70 bill

1. 20% of $70 = $14
2. 10% of $14 = $1.40
3. $14 - $1.40 = $12.60 (18%)

In practice, most people just calculate 20% and round down slightly. On a $70 bill, leaving $13 instead of $14 puts you right at 18.5%, which is close enough.

Tips for Making Mental Math Easier

Beyond the specific methods above, here are some general principles that make tip math faster and less stressful:

• Always round up, never down. Rounding up by a few cents costs you almost nothing but ensures you are tipping fairly. It also simplifies the numbers you are working with.
• Focus on the dollar amount, not the percentage. Once you have a tip amount that feels right, stop second-guessing the exact percentage. The difference between 18% and 19% on a $50 bill is fifty cents.
• Calculate on the pre-tax amount. Look at the subtotal line, not the total with tax. Tipping on the after-tax amount means you are tipping on the government's share, which inflates the real percentage.
• When in doubt, leave 20%. If you cannot decide between percentages or the math is getting too complicated, just double 10% and leave that. Twenty percent is generous, easy to calculate, and universally appreciated.
• Practice with everyday numbers. The next time you see a price tag, a grocery total, or a gas pump amount, mentally calculate 15% and 20%. The more you practice, the more automatic it becomes.

When Mental Math Is Not Enough

These tricks cover the vast majority of everyday tipping situations. But there are times when a calculator genuinely helps, especially when splitting a large bill among many people with different orders, calculating tips on bills over $500, or figuring out tips in a foreign currency where you are less comfortable with the denominations.

For those moments, our free tip calculator is always available. It handles custom percentages, bill splitting for any number of people, and gives you instant results. Bookmark it for when you need it, and use your mental math skills for everything else.