How to Get Faster at Mental Math: 9 Tricks That Work
To get faster at mental math, stop doing it the way paper taught you. Add from left to right, round to easy numbers and fix the difference, learn a few multiplication shortcuts, and break percentages into 10% chunks. Then drill for five minutes a day, because how to get faster at mental math is mostly about reps, not talent.
If numbers feel slow compared with the rest of your thinking, IQ Tester can show whether it is really your weak spot and give you a daily drill for it. Find my weak spots
Why speed is a habit, not talent
The friend who splits the Uber bill in two seconds is not a genius. They just have a few tricks on autopilot and have used them hundreds of times.
When you do mental math slowly, it is usually because you are:
- Running the written method in your head (carrying digits, lining up columns)
- Holding too many numbers at once
- Starting from scratch every time instead of using facts you already know
Every trick below fixes one of those. Pick two or three that fit what you do most (splitting bills, tips, sale prices, math class) and use them on purpose for a week. That is how to get good at mental math fast.
Add and subtract left to right
School teaches you to add from the right so you can carry. In your head, the left is easier because the big part lands first.
Trick 1: left-to-right addition
47 + 38
- Tens: 40 + 30 = 70
- Ones: 7 + 8 = 15
- 70 + 15 = 85
256 + 137: 200 + 100 = 300, 50 + 30 = 80, 6 + 7 = 13. So 300 + 80 + 13 = 393.
Trick 2: count up to subtract
1,000 − 368 feels ugly. Count up instead: 368 to 370 is 2, 370 to 400 is 30, 400 to 1,000 is 600. Total: 632. This is also how cashiers used to count change.
Round and fix
Trick 3: round, then correct
Numbers ending in 8 or 9 are annoying. Round them.
- $4.99 x 6: think $5 x 6 = $30, minus 6 cents = $29.94
- 63 − 29: 63 − 30 = 33, add 1 back = 34
- 148 + 199: 148 + 200 = 348, minus 1 = 347
This one trick handles a huge share of real-life shopping math.
Multiplication shortcuts
Trick 4: times 11 for two-digit numbers
Split the digits and put their sum in the middle.
- 43 x 11: 4 _ 3, and 4 + 3 = 7, so 473
- 87 x 11: 8 _ 7, 8 + 7 = 15. Put the 5 in the middle and carry the 1: 957
Trick 5: times 5, halve then times 10
- 5 x 68: half of 68 is 34, times 10 = 340
- 5 x 47: half of 47 is 23.5, times 10 = 235
Trick 6: double and halve
If one number is easy to halve and the other easy to double, do both.
- 16 x 25: 8 x 50 = 4 x 100 = 400
- 14 x 35: 7 x 70 = 490
Trick 7: break it apart
- 7 x 48: 7 x 50 = 350, minus 7 x 2 = 14, so 336
- 9 x 23: 10 x 23 = 230, minus 23 = 207
Trick 8: squaring numbers that end in 5
Take the first digit, multiply it by the next number up, then stick 25 on the end.
- 35²: 3 x 4 = 12, so 1,225
- 65²: 6 x 7 = 42, so 4,225
It is a flex in class, but it also helps you estimate areas fast.
Percentages in your head
Trick 9: build from 10%
Move the decimal one place left to get 10%. Everything else is built from there.
| You need | Do this | Example on $48 |
|---|---|---|
| 10% | Move decimal left | $4.80 |
| 5% | Half of 10% | $2.40 |
| 15% tip | 10% + 5% | $7.20 |
| 20% tip or 20% off | 10% x 2 | $9.60 |
| 25% off | Divide by 4 | $12 |
| 1% | Move decimal two places | $0.48 |
In the UK, VAT is 20%, so a price "ex VAT" plus 20% is just "add double the 10%." In Canada, tax is added at the register and differs by province, so know your rate and build it from 10% and 1% chunks. Sale shopping tip: 30% off a $60 hoodie is 3 x $6 = $18 off, so you pay $42.
Bonus: percentages flip. 8% of 50 is the same as 50% of 8, which is 4. Swap the numbers whenever one way is easier.
How to get faster at mental math: the 5-minute daily drill
Tricks mean nothing if you only read them. Here is a mental math practice routine you can do on the bus.
The routine
- Minute 1: warm-up. Add 10 random two-digit pairs, left to right.
- Minute 2: round and fix. Do 5 problems with 9s or 99s in them.
- Minute 3: multiply. Pick one trick (x11, x5 or double-and-halve) and do 6 problems.
- Minute 4: percentages. Look at any price near you and work out 15%, 20% and 25% off.
- Minute 5: speed round. Set a timer for 60 seconds and do as many times-table facts as you can. Write the count down.
Tracking that last number is the secret. If you do not write it down, you have no idea if you are getting faster.
Mental math games that count as practice
- Add up the numbers on license plates you pass
- Keep a running total of your shopping cart before checkout
- Play "make 24" with four random numbers from a deck of cards
- Race a friend on the bill split (then check with the calculator)
Where people stall
After two weeks many people plateau because they keep drilling the stuff they are already good at. The hard part is knowing which specific skill is slowing you down: working memory, number sense or just speed.
IQ Tester does that sorting for you. The two-minute check-in finds your weak spots, sometimes ranking you against people like you, then gives you one short drill a day and a score that shows whether you are actually getting quicker. It runs in the browser, no download, and the check-in is free. Find my weak spots
If word problems are the real issue, check out our 4-step method for math problem solving. For number patterns, try the logic puzzles for teens.
Get quicker with numbers this week
That is how to get faster at mental math: left-to-right adding, round and fix, a few multiplication shortcuts, percentages from 10%, and five minutes a day that you actually track. In the next two minutes, IQ Tester's free check-in can show whether number speed is really your weak spot and give you a daily drill to fix it.
FAQ
How can I get better at mental math fast?
Pick two or three tricks that match what you do most, like round-and-fix and percentages from 10%, and use them every chance you get for a week. Add a 5-minute daily drill and write down your speed-round score. Most people notice they are quicker within a couple of weeks.
What is the fastest way to do mental math quickly?
Work left to right, round awkward numbers and fix the difference, and use facts you already know instead of carrying digits. The more automatic your times tables are, the faster everything else gets.
How do I calculate a tip in my head?
Find 10% by moving the decimal one place left. For 15%, add half of that again; for 20%, double it. On a $36 bill, 10% is $3.60, so a 20% tip is $7.20.
Are mental math games good practice?
Yes, as long as you are actually calculating and not guessing. Games like "make 24," adding license plates or racing a friend on the bill split build speed and number sense. Pair them with a short tracked drill so you can see progress.
Is mental maths the same as mental math?
Yes. "Mental maths" is how people say it in the UK (and Australia), while the US and Canada usually say "mental math." The tricks work the same either way.