ASVAB Math Without a Calculator: 15 Mental Math Tricks to Boost Your Score

Wait, No Calculator? Don't Panic.

Let's address the elephant in the room: Yes, you cannot use a calculator on the ASVAB. No phones, no smartwatches, no fancy TI-84 you relied on in high school. Just you, your brain, and some scratch paper.

If that just made your stomach drop, take a breath. You're not alone. Most people taking the ASVAB haven't done mental math since middle school. We've all gotten used to reaching for our phones to split a restaurant bill.

But here's the thing—the ASVAB isn't trying to trick you with impossible calculations. The test writers know you don't have a calculator. That means the numbers are usually designed to work out nicely. You just need the right shortcuts to get there.

In this guide, I'm going to share 15 mental math tricks that will make ASVAB math feel way less scary. These aren't complicated strategies that require memorizing a textbook. They're simple techniques you can start using today.

Ready? Let's do this.

Why the ASVAB Tests Math This Way

Before we dive into the tricks, you might be wondering: "Why can't I just use a calculator like a normal person in 2025?"

Here's why the military cares about mental math:

1. Real-world problem solving - In the field, you won't always have technology handy
2. Quick thinking - The military values people who can think fast under pressure
3. Foundational skills - Understanding math concepts matters more than calculator button-pushing
4. Fairness - Everyone takes the test under the same conditions

The ASVAB isn't testing whether you can punch numbers into a calculator. It's testing whether you can think through problems logically. And honestly? Once you learn these tricks, you might find mental math is faster than using a calculator anyway.

Check out our full ASVAB study guide for more preparation tips.

15 Mental Math Tricks for ASVAB Success

Trick #1: Multiply by 5 the Easy Way

The problem: Multiplying by 5 can feel awkward, especially with bigger numbers.

The trick: Multiply by 10 first, then divide by 2.

Why it works: 5 is half of 10. So multiplying by 10 (just add a zero) and halving is way easier than multiplying by 5 directly.

Example:

• 48 × 5 = ?
• Step 1: 48 × 10 = 480
• Step 2: 480 ÷ 2 = 240

Another example:

• 126 × 5 = ?
• Step 1: 126 × 10 = 1,260
• Step 2: 1,260 ÷ 2 = 630

This works every single time, and it's way faster than traditional multiplication.

Trick #2: The 10% Shortcut for Percentages

The problem: Percentage problems trip up a lot of test-takers.

The trick: Find 10% first, then adjust from there.

Why it works: 10% of any number is just moving the decimal one place left. From there, you can build any percentage.

Example: What is 30% of 80?

• 10% of 80 = 8
• 30% = 3 × 10%, so 3 × 8 = 24

Example: What is 15% of 200?

• 10% of 200 = 20
• 5% = half of 10% = 10
• 15% = 20 + 10 = 30

Example: What is 25% of 60?

• 10% of 60 = 6
• 25% = 10% + 10% + 5% = 6 + 6 + 3 = 15
• (Or remember that 25% = 1/4, so 60 ÷ 4 = 15)

Trick #3: Memorize These Fraction-to-Decimal Conversions

The problem: Converting between fractions and decimals takes too long.

The trick: Memorize the common conversions cold.

Why it matters: When you see these fractions in a problem, you can instantly convert them without calculating.

Trick #4: Estimate First, Then Eliminate

The problem: You're not sure if your answer is right.

The trick: Before calculating exactly, estimate to eliminate obviously wrong answers.

Example: A store sells 47 items at $19 each. What's the total?

Before calculating exactly:

• 47 is close to 50
• 19 is close to 20
• 50 × 20 = 1,000

So your answer should be slightly less than 1,000. If you see answer choices like:

• A) 423
• B) 893
• C) 1,247
• D) 1,893

You can immediately eliminate A (way too low) and D (way too high). Your answer is probably B or C, but closer to 1,000, so B) 893 is most likely.

This works especially well when you're short on time.

Trick #5: Break Apart Big Numbers

The problem: Large multiplication problems look intimidating.

The trick: Break numbers into easier pieces using the distributive property.

Example: 23 × 7 = ?

• Break 23 into 20 + 3
• 20 × 7 = 140
• 3 × 7 = 21
• 140 + 21 = 161

Example: 45 × 12 = ?

• Break 12 into 10 + 2
• 45 × 10 = 450
• 45 × 2 = 90
• 450 + 90 = 540

This technique turns scary problems into simple ones.

Trick #6: Squaring Numbers Ending in 5

The problem: Squaring numbers takes forever.

The trick: For any number ending in 5, there's a pattern.

The rule:

1. Take the digit(s) before the 5
2. Multiply that number by (itself + 1)
3. Put 25 at the end

Example: 35²

• First digit: 3
• 3 × 4 = 12
• Add 25 to the end: 1,225

Example: 75²

• First digit: 7
• 7 × 8 = 56
• Add 25 to the end: 5,625

Example: 15²

• First digit: 1
• 1 × 2 = 2
• Add 25: 225

Works every time!

Trick #7: The 9s Multiplication Finger Trick

The problem: The 9 times table is tricky.

The trick: Use your fingers (yes, really).

How it works:

1. Hold up both hands, palms facing you
2. For 9 × N, put down finger number N (counting from left)
3. The fingers to the LEFT of the down finger = tens digit
4. The fingers to the RIGHT = ones digit

Example: 9 × 7

• Put down finger #7 (ring finger on right hand)
• 6 fingers to the left = 6 tens
• 3 fingers to the right = 3 ones
• Answer: 63

Alternatively, remember: 9 times any single digit, the digits always add up to 9.

• 9 × 2 = 18 (1+8=9)
• 9 × 7 = 63 (6+3=9)
• 9 × 8 = 72 (7+2=9)

Trick #8: Turn Word Problems into Equations

The problem: Word problems are confusing with all that text.

The trick: Learn to translate key phrases into math symbols.

Example: "What is 15% of 80?"

• "What" = x
• "is" = =
• "15%" = 0.15
• "of" = ×
• Translation: x = 0.15 × 80 = 12

Example: "A number decreased by 7 equals 15"

• "A number" = x
• "decreased by" = -
• "equals" = =
• Translation: x - 7 = 15, so x = 22

Practice more Arithmetic Reasoning problems

Trick #9: Work Backwards from Answer Choices

The problem: You're stuck and don't know how to start.

The trick: Plug answer choices back into the problem to see which works.

Example: If 3x + 7 = 22, what is x?

• Try choice B (let's say it's 5): 3(5) + 7 = 15 + 7 = 22 ✓

This is especially useful for complex equations where you're not sure of the steps.

Pro tip: Start with choice B or C (middle values). If the result is too high, try a smaller number. If too low, try bigger.

Trick #10: The Cross-Multiplication Shortcut

The problem: Comparing or solving fractions takes too long.

The trick: Cross-multiply to compare or solve proportions instantly.

To compare fractions: Which is bigger, 3/7 or 5/11?

• Cross multiply: 3 × 11 = 33 and 7 × 5 = 35
• Since 33 < 35, we know 3/7 < 5/11

To solve proportions: If 3/4 = x/20, find x.

• Cross multiply: 3 × 20 = 4 × x
• 60 = 4x
• x = 15

Trick #11: Unit Conversion Shortcuts

The problem: Converting between units is confusing.

The trick: Set up conversion fractions so unwanted units cancel out.

Memorize these:

• 1 foot = 12 inches
• 1 yard = 3 feet
• 1 mile = 5,280 feet
• 1 hour = 60 minutes
• 1 minute = 60 seconds

Example: Convert 15 feet to inches.

• 15 feet × (12 inches/1 foot) = 15 × 12 = 180 inches

Example: How many feet is 2 miles?

• 2 miles × 5,280 feet/mile = 10,560 feet

Trick #12: The Subtraction Trick for Making Change

The problem: Subtracting from numbers like 100 or 1,000 is awkward.

The trick: Subtract from (number - 1), then add 1 to the last digit.

Example: 1,000 - 387

• Subtract from 999 instead: 999 - 387 = 612
• Add 1: 613

Example: 100 - 47

• Subtract from 99: 99 - 47 = 52
• Add 1: 53

Why? Because subtracting from all 9s is easier (no borrowing needed).

Trick #13: Doubling and Halving for Multiplication

The problem: Some multiplication combinations are just hard.

The trick: Double one number and halve the other—the product stays the same.

Example: 25 × 16 = ?

• Double 25 → 50
• Halve 16 → 8
• 50 × 8 = 400

Example: 35 × 4 = ?

• Double 35 → 70
• Halve 4 → 2
• 70 × 2 = 140

This is especially helpful when you can get one number to 10, 50, or 100.

Trick #14: Adding/Subtracting Fractions Fast

The problem: Finding common denominators takes forever.

The trick: Use the "bowtie" method for quick addition/subtraction.

The bowtie method:

1. Cross multiply diagonally to get the numerators
2. Multiply denominators for the new denominator
3. Add (or subtract) the numerators

Example: 2/3 + 3/5

• Numerators: (2 × 5) and (3 × 3) = 10 and 9
• Add numerators: 10 + 9 = 19
• New denominator: 3 × 5 = 15
• Answer: 19/15 or 1 4/15

Example: 5/6 - 1/4

• Numerators: (5 × 4) and (1 × 6) = 20 and 6
• Subtract: 20 - 6 = 14
• Denominator: 6 × 4 = 24
• Answer: 14/24 = 7/12 (simplified)

Trick #15: The "Is Over Of" Percentage Formula

The problem: Percentage word problems are confusing.

The trick: Use the formula: Part/Whole = Percent/100

Or remember: "Is" over "Of" equals percent over 100

Example: 15 is what percent of 60?

• "15" is the "is" (part)
• "60" is the "of" (whole)
• 15/60 = x/100
• Cross multiply: 1500 = 60x
• x = 25%

Example: What is 40% of 75?

• x/75 = 40/100
• 100x = 3000
• x = 30

Practice Problems: Test Your New Skills

Let's put these tricks to work. Try solving these without a calculator:

Problem 1: A recruit runs 6 miles in 48 minutes. At this pace, how long would it take to run 10 miles?

Problem 2: What is 35% of 80?

Problem 3: If a $240 jacket is on sale for 25% off, what's the sale price?

Problem 4: Solve: 125 × 8

Problem 5: If 4/5 of the soldiers in a unit are on duty and there are 200 soldiers total, how many are on duty?

Solutions:

Problem 1: Set up a proportion: 6/48 = 10/x. Cross multiply: 6x = 480, x = 80 minutes.

Problem 2: Using the 10% trick: 10% of 80 = 8, so 35% = 8 + 8 + 8 + 4 = 28. (Or: 30% = 24, plus 5% = 4, total = 28)

Problem 3: 25% off = 75% of original price. 75% of 240: 10% = 24, so 75% = 24 × 7.5 = $180. (Or 240/4 = 60 off, so 240 - 60 = $180)

Problem 4: Using doubling/halving: 125 × 8 = 250 × 4 = 500 × 2 = 1,000

Problem 5: 4/5 of 200 = (200 ÷ 5) × 4 = 40 × 4 = 160 soldiers

How to Practice Mental Math Daily

Knowing these tricks is one thing. Making them automatic is another. Here's how to build your mental math muscles:

1. Practice During Daily Life

• Calculate tips in your head at restaurants (use the 10% trick!)
• Estimate your grocery total before checkout
• Figure out sale prices without your phone

2. Use Timed Practice

• Set a timer for 5 minutes
• Do as many problems as you can
• Speed builds confidence

3. Review Mistakes

• When you get something wrong, figure out why
• Which trick could have helped?
• Practice that specific type of problem

4. Take Practice Tests

• Nothing beats realistic practice
• Time yourself like the real test
• Learn to pace yourself

Start practicing ASVAB math questions now

Key Takeaways

Here's what to remember:

• No calculator? No problem. The ASVAB math is designed to be doable without one.
• Estimation is your friend. When in doubt, estimate to eliminate wrong answers.
• Memorize the basics. Know your multiplication tables, common fractions, and key formulas.
• Break problems down. Big numbers become easy when you split them apart.
• Practice makes permanent. The more you use these tricks, the more automatic they become.

The ASVAB math sections aren't about testing whether you're a genius. They're about testing whether you can think logically and work efficiently. With these 15 tricks in your toolkit, you've got everything you need to crush it.

Now stop reading and start practicing. Your future military career is waiting.

Take a free ASVAB practice test now

*Want more ASVAB prep tips? Check out our complete 2025 ASVAB study guide or practice with hundreds of realistic questions.*