Mental Math Shortcuts: How to Calculate Faster in Your Head

I am NOT a math person. Like, at all. In school, I was that kid who needed a calculator for everything. Even basic addition sometimes. I just... numbers don't click for me the way they do for some people.

My math teacher in high school (Mrs. Patterson, if you're reading this, I'm sorry) used to get so frustrated with me. "Sarah, you're smart, why can't you do this?" I don't know, Mrs. Patterson, I just can't!

But then I learned some mental math tricks. Like, actual shortcuts that make math easier. And everything changed. Not like "I'm a math genius now" changed, but like "I can calculate a 20% tip without pulling out my phone" changed. Which is still pretty cool.

I'm still not a math person. But I know some tricks. And that's enough for me.

Here are the ones that actually work (and that I can actually remember).

The 9's Trick (My Favorite)

Okay so this is my absolute favorite trick. To multiply any number by 9, there's this super easy way:

For 9 × 8: - Take the number (8), subtract 1 = 7 (that's your tens digit) - Then 10 minus the number (10 - 8) = 2 (that's your ones digit) - Answer: 72

Try it with 9 × 7: - 7 - 1 = 6 - 10 - 7 = 3 - Answer: 63

It works for any single digit! I use this ALL the time. Like, constantly. It's so much faster than actually multiplying.

My friend showed me this trick and I felt like my mind was blown. How did I not know this? How did I make it through school without learning this? I have no idea. But now I know it, and I use it constantly.

Multiplying by 11

This is surprisingly easy. To multiply a two-digit number by 11:

For 23 × 11: - Add the digits: 2 + 3 = 5 - Put that in the middle: 2 5 3 - Answer: 253

If the sum is 10 or more, you carry over: For 57 × 11: - 5 + 7 = 12 - Put 2 in the middle, carry the 1: 6 2 7 - Answer: 627

Squaring Numbers Ending in 5

This is almost too easy. To square any number ending in 5:

For 25²: - Take the first digit (2), multiply by the next number (3): 2 × 3 = 6 - Put 25 at the end: 625

For 45²: - 4 × 5 = 20 - Put 25 at the end: 2025

Percentages

Calculating percentages is easier than most people think:

10%: Just move the decimal one place left - 10% of 250 = 25.0

5%: Half of 10% - 5% of 250 = 12.5

20%: Double 10% - 20% of 250 = 50

15%: 10% + 5% - 15% of 250 = 25 + 12.5 = 37.5

Tips

For a 20% tip, just move the decimal and double: - Bill is $45.00 - 10% = $4.50 - 20% = $9.00

For 15%, it's 10% + half of 10%: - Bill is $45.00 - 10% = $4.50 - Half = $2.25 - 15% = $6.75

Multiplying by 5

Instead of multiplying by 5, multiply by 10 and divide by 2: - 24 × 5 = 24 × 10 ÷ 2 = 240 ÷ 2 = 120

Dividing by 5

Instead of dividing by 5, multiply by 2 and divide by 10: - 240 ÷ 5 = 240 × 2 ÷ 10 = 480 ÷ 10 = 48

Adding Large Numbers

Break them into easier chunks: - 347 + 258 - Think: 300 + 200 = 500 - Then: 47 + 58 = 105 - Total: 500 + 105 = 605

Subtracting

Use the "complement" method: - 1000 - 347 - Think: What plus 347 equals 1000? - 347 + 653 = 1000 - Answer: 653

Multiplying Two-Digit Numbers

There's a trick for numbers close to 100: - 98 × 97 - Both are close to 100 - 98 is 2 away from 100, 97 is 3 away - Subtract one number's distance from the other: 98 - 3 = 95 (or 97 - 2 = 95) - Multiply the distances: 2 × 3 = 6 - Answer: 9506 (put 06, not just 6)

Practice (The Boring But Necessary Part)

So these tricks are great, but you actually have to practice them. I know, I know—practice is boring. But it's necessary.

I practice mental math basically every day. Not like, formal practice sessions. Just... when I'm walking, I'll calculate things. When I'm waiting in line, I'll do math in my head. When I'm bored, I'll practice our Speed Math game—it's actually fun once you get into it. It's become kind of a habit, actually.

Start with the easy ones. Percentages are super easy once you get the hang of it. Multiplying by 11 is also pretty straightforward. Master those, then move on to the harder ones.

Don't try to learn them all at once. I made that mistake. I tried to memorize like 10 different tricks in one day, and I remembered... maybe 2 of them? Not great. Pick one or two, practice them until they're automatic, then add another one.

It takes time. But once you get them down, they're yours forever. And honestly? It's kind of satisfying to be able to do math in your head. Makes you feel smart, even if you're not actually a math person.

Real-World Applications

Here's where these tricks come in handy:

• Shopping: Quick price comparisons
• Restaurants: Calculating tips and splitting bills
• Cooking: Adjusting recipes
• Time management: Quick calculations
• Games: Our Speed Math game is way easier now (and more fun!)

The Bottom Line

So here's the thing: you don't need to be a math genius to do mental math. You just need to know some tricks and actually practice them.

Start with the easy ones (percentages, multiplying by 11). Practice regularly (even just a few minutes a day). And don't be afraid to use a calculator when you need to—these are shortcuts, not replacements for all math.

But for quick calculations? These tricks are way faster than pulling out your phone. And honestly? It's kind of impressive when you can calculate a tip or split a bill in your head. People are like "how did you do that?" and you get to feel smart for a second.

Plus, they're actually kind of fun once you get the hang of them. Like a little mental puzzle. Who would have thought math could be fun? Not me, that's for sure.