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How to calculate a discount in your head

Work out the discount, then take it off. Or skip a step: at 25% off, you pay 75%.

Find the discount, then take it off

Work out the percent off, then subtract it from the price.

1. $60 − 30%
2. 10% = $6
3. 30% = $18
4. $60 − $18 = $42

Why it works: What you pay is the price minus what you save.

Or work out what you pay

25% off means you pay the other 75%: three quarters of the price.

1. $80 − 25%
2. $80 ÷ 4 = $20
3. $20 × 3 = $60

Why it works: 100% − 25% = 75%, and 75% is ¾.

Two discounts don't add up

20% off and then another 10% off is 28% off, not 30%.

1. $100 − 20%
2. $100 − $20 = $80
3. $80 − 10%
4. $80 − $8 = $72

Why it works: The second discount comes off the lower price, so it saves less.

Is it a deal? Compare the price of one

Divide a multi-buy price by how many you get, and compare it with the single price.

1. 3 for $5
2. $5 ÷ 3 ≈ $1.67
3. $1.67 < $1.80

Why it works: Prices only compare for the same amount.

Try it

Tap a problem to check your answer.

$45 at 20% off

= $36

$60 at 25% off

= $45

$72 at 10% off

= $64.80

$35 at 40% off

= $21

More money math: Tip math · Splitting a bill · Comparing prices

In Math Daily, Perci asks problems like these: tips, discounts and splitting the bill, alongside fractions and percents.

Common questions

How do I calculate a percent off?

Multiply the price by the percent to get the discount, and subtract it. Or multiply by what's left: 30% off means paying 70% of the price.

What's 30% off $50?

$15 off, so you pay $35.