Everyday Math Examples

You use math every day, usually without calling it math. Working out a sale price, splitting a bill, doubling a recipe or checking whether a pay rise beats inflation are all everyday math. This guide works through 12 everyday math examples with real numbers, showing the sum for each one and the tool that does it for you.

Shopping

1. Working Out a Discount

A jacket is $80 with 30% off. Discount = 80 × 0.30 = $24, so you pay 80 − 24 = $56. A quicker way is 80 × 0.70 = $56.

Watch out for stacked discounts. “20% off, plus an extra 10% at the till” is not 30% off. You pay 80% and then 90% of that: 0.80 × 0.90 = 0.72, which is 28% off. The discount calculator handles both.

2. Comparing Unit Prices

Which is better value: 750 g of coffee for $4.50, or 1.2 kg for $6.20?

4.50 ÷ 7.5 = $0.60 per 100 g
6.20 ÷ 12 = about $0.52 per 100 g

The bigger bag is cheaper per gram. Bigger is not always better value, though, so it pays to check. A unit price calculator does this for any two sizes.

3. Adding Sales Tax

A $45 item with 6% sales tax costs 45 × 1.06 = $47.70. To find the price before tax on a receipt, divide instead: $47.70 ÷ 1.06 = $45. The sales tax calculator does both.

Eating Out

4. Calculating a Tip

On a $64 bill, an 18% tip is 64 × 0.18 = $11.52, making the total $75.52.

A mental shortcut: 10% of $64 is $6.40. Double it for 20% ($12.80), or add half again for 15% ($9.60). The tip calculator also splits the total between people and can round each share up.

5. Splitting a Bill Fairly

Three friends have a $96 bill. Sam’s food came to $40, Ali’s to $32 and Jo’s to $24. They want to add a 20% tip.

Each person multiplies their own share by 1.20:

Sam: 40 × 1.20 = $48.00
Ali: 32 × 1.20 = $38.40
Jo: 24 × 1.20 = $28.80

Check: 48 + 38.40 + 28.80 = $115.20, which is $96 plus 20%. Splitting by what each person ordered is fairer than an even split when orders are very different.

Cooking

6. Scaling a Recipe

A recipe for 4 needs 3/4 cup of milk, and you are cooking for 6. That is 6 ÷ 4 = 1 1/2 times the recipe.

3/4 × 1 1/2 = 3/4 × 3/2 = 9/8 = 1 1/8 cups.

The fraction calculator works with mixed numbers like 1 1/2, so you do not have to convert them first.

Money

7. Setting a Monthly Budget

The 50/30/20 rule splits take-home pay into needs, wants and savings. On $4,000 a month after tax:

Needs (50%): $2,000 for rent, bills, groceries and transport
Wants (30%): $1,200 for eating out, hobbies and subscriptions
Savings and debt (20%): $800

It is a starting point, not a rule. In a high-rent area, needs often take more than half. Use the percentage calculator to see what share of your pay each bill takes.

8. Checking a Pay Rise

Your salary goes from $52,000 to $54,080. (54,080 − 52,000) ÷ 52,000 × 100 = 4% rise.

If prices rose by more than 4% over the same year, your pay buys less than before, even though the number went up. The percentage change calculator shows the exact change between any two figures.

9. Interest on Savings

$5,000 in a savings account at 4% a year:

Simple interest for one year: 5,000 × 0.04 = $200
Compounded monthly for one year: 5,000 × (1 + 0.04/12)¹² ≈ $5,203.71, which is $203.71 of interest

The extra $3.71 comes from earning interest on the interest. Over many years, that difference grows much larger.

Travel

10. Working Out Fuel Cost

A 300-mile trip in a car that does 30 miles per gallon, with fuel at $3.50 a gallon:

Fuel needed = 300 ÷ 30 = 10 gallons. Cost = 10 × 3.50 = $35.

If four people share the drive, that is $8.75 each.

11. Estimating Travel Time

150 miles at an average of 60 mph takes 150 ÷ 60 = 2.5 hours, which is 2 hours 30 minutes. Remember that 0.5 hours is 30 minutes, not 50.

For physics-style questions with direction and acceleration, use the velocity calculator.

Home and DIY

12. Buying Flooring for a Room

A room is 12 ft × 10 ft. Area = 12 × 10 = 120 sq ft. Add 10% for cuts and waste: 120 × 1.10 = 132 sq ft.

If flooring comes in packs of 20 sq ft, you need 132 ÷ 20 = 6.6, so buy 7 packs. Always round up when buying materials.

Other Numbers You Check Without Noticing

Your age in days or the days to a birthday. The age calculator counts them exactly, including leap years.
Your BMI. It is weight divided by height squared, which the BMI calculator works out in US or metric units.
Daily calories. The calorie calculator estimates how much energy you use in a day from your size and activity.

How to Get Faster at Everyday Math

Learn the 10% trick. Moving the decimal point one place left gives 10% of anything. Most other percentages can be built from it.
Round first, then adjust. $19.95 × 4 is close to $20 × 4 = $80, minus 4 × 5 cents, which is $79.80.
Estimate before you calculate. If your answer is far from your estimate, check the sum again.
Know your formulas. Our list of basic math formulas covers area, percentages, averages and interest.