How to Calculate 30% Off and Other Discounts

This article is part of Money Basics. It helps you read sale signs, do quick math, and decide if a deal is worth it.

1) What you'll learn

What “30% off” means in plain words
How to find the discount amount and the sale price
Easy tricks for percent math in your head
How stacked discounts work (like 30% off + 10% off)
The truth about “Buy one, get one 50% off”
How tax and shipping can change the final price
How to compare two deals and pick the better one

2) Concept explanation

When a store says “30% off,” it means you pay 30% less than the original price. A percent is a part out of 100. So 30% means 30 out of 100 parts.

Think of a dollar as 100 small cents. If you take 30% off, you remove 30 of those 100 parts. You only pay the other 70 parts. So 30% off means you pay 70% of the price.

Here is a simple picture in words. Imagine a $10 pizza cut into 10 slices. Each slice is$ 1. Thirty percent off is like removing 3 slices ( $3). You pay for 7 slices ($ 7). Same idea for any price. Remove 30% of it, and you pay the rest.

Sales can use many words: “off,” “markdown,” “sale price,” or “clearance.” They all mean the price goes down from the original price. Your goal is to find the new price quickly and know if the deal helps your budget.

3) Why it matters

You have limited money. Maybe you get an allowance. Maybe you save for a game, shoes, or a gift. When you understand discounts, you can stretch your money. A small mistake can cost you a few dollars. Many small mistakes add up.

Stores use big sale signs to get your attention. Some deals are great. Some only look great. If you can do the math, you can avoid traps. You will know when to buy now and when to wait.

Also, discounts show up everywhere. Online shops. App stores. Food delivery. Even school fundraisers. If you can compare two offers, you can choose the best one and feel proud of your smart choice.

4) Calculation method

Let’s learn two key ideas: discount amount and sale price.

Discount amount: how much money you save.
Sale price: what you pay after the discount.

Formulas:

Discount Amount = Original Price × Discount Rate Sale Price = Original Price × (1 − Discount Rate)

Tip: Write percent as a decimal for the formulas.

30% = 0.30
25% = 0.25
10% = 0.10

Step-by-step for 30% off:

Find 10% of the price. Move the decimal one place left.
Multiply by 3 to get 30%.
Subtract that from the original price.

Example A: A $50 game is 30% off.

10% of $50 is$ 5.
30% is 3 × $5 =$ 15.
Sale price = $50 −$ 15 = $35.

Example B: A $20 T-shirt is 25% off.

10% of $20 is$ 2.
5% is half of 10%: $1.
25% is 10% + 10% + 5% = $2 +$ 2 + $1 =$ 5.
Sale price = $20 −$ 5 = $15.

Example C: A $80 pair of shoes is 40% off.

10% of $80 is$ 8.
40% is 4 × $8 =$ 32.
Sale price = $80 −$ 32 = $48.

Mental math hacks:

50% off = half the price.
25% off = quarter of the price.
20% off = 10% × 2.
15% off = 10% + 5%.
30% off = 10% × 3.

Stacked discounts (two discounts in a row):

“30% off + extra 10% off” is not 40% off.
You take 10% off the already reduced price.

Steps for stacked discounts:

Apply the first discount to get a new price.
Apply the second discount to the new price.

Example D: $100 jacket, 30% off, then extra 10% off.

First discount: 30% of $100 =$ 30. New price = $70.
Second discount: 10% of $70 =$ 7. Final price = $70 −$ 7 = $63.
Total saved = $37, which is 37% off, not 40%.

“Buy one, get one 50% off” (BOGO 50%):

You pay full price for the first item.
You get 50% off the second item.
Average discount is less than 50%.

Example E: Two $30 shirts, BOGO 50%.

First shirt: $30.
Second shirt: $15 (half of$ 30).
Total = $45 for two shirts.
Average price per shirt = $22.50.
Effective discount per shirt = $7.50 saved from$ 30, which is 25% off on average.

Reverse problem (harder but useful):

You know the sale price and the discount percent.
You want to find the original price.

Use this formula:

Original Price = Sale Price ÷ (1 − Discount Rate)

Example F: Sale price is $35 after 30% off. What was original?

1 − 0.30 = 0.70.
Original = $35 ÷ 0.70 =$ 50.

Quick checks to avoid mistakes:

If discount is 30%, the sale price should be 70% of the original.
Sale price must be less than the original price.
If your answer goes up, re-check your math.

5) Case study

Story: Maya is saving for a new hoodie. The tag says $60. She has$ 50. The store has a sign: “30% off today!” There is also a small note: “Extra 10% off with student ID.” Sales tax in her town is 8%. Does she have enough?

Step 1: First discount (30% off)

10% of $60 is$ 6.
30% is 3 × $6 =$ 18.
New price after 30% off = $60 −$ 18 = $42.

Step 2: Second discount (extra 10% off)

10% of $42 is$ 4.20.
New price = $42 −$ 4.20 = $37.80.

Step 3: Add sales tax (8%)

Tax is on the price you pay, not the original tag.
10% of $37.80 is$ 3.78. 8% is a bit less.
To be exact: $37.80 × 0.08 =$ 3.024. Round to $3.02 or$ 3.03 depending on store rounding.
Total with tax ≈ $37.80 +$ 3.02 = $40.82.

Maya’s total is about $40.82. She has$ 50. She has enough money. She even has money left for a snack.

Think about it:

If tax was 0%, what would her total be?
If there was no student discount, would she still have enough?

Extra case: Online vs store

Online price: $38, free shipping, no extra discount, same 8% tax.
Store price we found: about $40.82.
Online total: $38 × 1.08 =$ 41.04.
The store is cheaper this time. Surprising, right? Always do the math.

6) Practical applications

Compare two discounts: Which is better, 25% off or $10 off? Example: Original price$ 50.
- 25% off = $12.50 off. New price =$ 37.50.
- $10 off =$ 40.
- Better deal: 25% off in this case.
Pick when to buy: If your item is $30 and 15% off today, is it worth it?
- 10% is $3. 5% is$ 1.50.
- 15% off saves $4.50. New price =$ 25.50. If you need it now and it fits your budget, buy it. If not urgent, you can wait for a bigger sale.
Budget for tax and shipping:
- If your budget is $25, aim for an item priced around$ 22 before an 8% tax.
- Shipping can erase a discount. A $5 ship fee can wipe out a 20% discount on a$ 20 item.
Understand “up to” sales:
- “Up to 50% off” means some items get 50%, many get less.
- Check the tag on your item, not just the big sign.
Check unit price:
- A big bottle 20% off might still cost more per ounce than a small bottle at regular price.
- Look at the price per ounce or per count when possible.
Plan your buy with stacked deals:
- Use store sale first, then a coupon percent off, then a dollar-off coupon last if allowed.
- Percent-off coupons usually work better on higher prices. Dollar-off coupons are better on smaller totals.

Quiz yourself:

A $40 hoodie is 30% off. What is the sale price?
A $25 game has 20% off plus an extra 10% off. What is the final price before tax?
Two snacks cost $3 each. The deal is “Buy one, get one 50% off.” What is the total?

Check your thinking:

1. 10% of $40 is$ 4. 30% is $12. Sale price =$ 28.
1. First 20% off: 10% is $2. So 20% is$ 4. New price = $21. Extra 10% off:$ 2.10. Final = $18.90.
1. First snack $3. Second is$ 1.50. Total = $4.50.

7) Common misconceptions

よくある誤解

- Thinking 30% off + 10% off = 40% off. It is less. You discount the new price, not the original. - Forgetting tax and shipping. A “deal” can cost more in the end. - Mixing up percent and dollars. “20 off” is not the same as “20% off.” - Assuming “Buy one, get one 50% off” is 50% off everything. It averages to 25% off if prices match. - Believing “up to 70% off” applies to every item. It often applies to very few items.

8) Summary

まとめ

- 30% off means you pay 70% of the original price. - Discount Amount = Original × Discount Rate. Sale Price = Original × (1 − Rate). - Use 10% chunks for fast mental math. - Stacked discounts multiply, they do not add. - "Buy one, get one 50% off" is about 25% off on average for two same-price items. - Always add tax and shipping before you decide. - Compare deals with simple steps and pick what fits your budget.

Practice makes discount math fast. Try doing 10% in your head, then build from there. Soon, sales signs will feel like secret codes you can read!

Glossary

Percent: A part out of 100. For example, 30% means 30 out of 100.

Discount: A price reduction from the original price.

Original Price: The starting price before any discounts.

Sale Price: The price after the discount is taken off.

Discount Rate: The percent used to reduce the price, like 30%.

Stacked Discounts: Two or more discounts used one after another.

Sales Tax: Extra percent added by the government on most purchases.

BOGO: Short for Buy One, Get One. A common sale type.

Calculating Discounts: What Does 30% Off Mean?