What this calculator does
Find out what a "buy one, get one" deal is really worth. Enter the regular price and the terms of the deal. The calculator shows the real percent off and the real price of each item you take home.
Multi-buy deals can be hard to compare with a normal sale. Is "buy 2, get 1 free" better than 30% off? This page answers that by spreading the savings over every item. It also compares the deal with a straight percent off, if you enter one.
Where it's used
Why this math matters outside the classroom:
- Grocery shopping. A shopper sees buy 2, get 1 free on $4.50 cereal: 3 boxes for $9.00 is $3.00 a box, one third off.
- Comparing sales. Buy 1, get 1 half off two $40 shoes costs $60, which is 25% off and more than a 30% off sale at $56.
- Stocking up. Families buy 3, get 1 free on $8 detergent, paying $24 for 4 bottles, or $6 each.
- Classroom percents. Students turn buy one, get one free into a percent by dividing the $1 saved on every $2 of goods.
Grade level and standards: Grade 7; Common Core State Standards for Mathematics 7.RP.A.3. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the regular price of one item.
- Enter how many you buy at full price and how many you get at the deal price.
- Enter the discount on the extra items: 100% if they're free, 50% if they're half off.
- Add another percent-off offer to compare, or leave it blank.
What the inputs mean
- Regular price of one item
- The normal price of one item before any deal. This assumes every item costs the same.
- Buy this many at full price
- In "buy 2, get 1 free", this is the 2.
- Get this many at the deal price
- In "buy 2, get 1 free", this is the 1.
- Discount on those extra items
- How much is taken off each extra item. Free is 100%. Half price is 50%.
- Compare with a straight percent off (optional)
- A plain sale on the same items, such as 40% off everything. The calculator tells you which deal costs less for the same number of items.
Formula and method
items you take home = items you buy + items you get you pay = price × items you buy + price × items you get × (1 − discount ÷ 100) real percent off = (regular total − what you pay) ÷ regular total × 100 real price per item = what you pay ÷ items you take home
The trick is to look at the whole bundle. A "buy one, get one free" deal gives you two items for the price of one. Spread over both items, that's the same as 50% off each one.
The calculator works out what all the items would cost at the regular price. Then it works out what you actually pay with the deal. The gap is your savings. Dividing the savings by the regular total gives the real percent off.
To compare with a straight sale, it takes the other percent off the regular total for the same number of items. Whichever total is lower is the better deal, as long as you want all the items.
Worked example
A $30 item is on a "buy one, get one free" deal. Another offer is 40% off.
- Items you take home: 1 + 1 = 2.
- Regular price for both: $30 × 2 = $60.
- With the deal you pay $30 × 1 + $0 × 1 = $30, so you save $30.
- Real percent off: $30 ÷ $60 × 100 = 50%. Each item really costs $30 ÷ 2 = $15.
- At 40% off, two items cost $60 × 0.6 = $36, which is $6 more.
Result: Buy one, get one free is 50% off each item, or $15 apiece. For two items, it beats 40% off by $6.00.
Understanding the result
A multi-buy deal only saves money if you'll use the extra items. If you need just one, the deal costs you the full $30, while 40% off would cost $18. Look at the "cost if you only needed" line before you buy.
"Buy one, get one 50% off" sounds like half off, but it works out to only 25% off each item. That's because the discount applies to just one of the two items.
Free items are worth the most when the thing keeps well or you'd buy it anyway, like soap or batteries. They're worth less for food that might spoil before you use it.
Assumptions and limitations
- Every item has the same regular price.
- The deal applies once to the number of items you enter. For more sets, scale the numbers up, since the percent off stays the same.
- Sales tax is left out. At one tax rate it doesn't change which deal is cheaper.
- When items have different prices, stores often make the cheapest one free or discounted. This calculator doesn't handle mixed prices.
- Some deals have limits or need a membership or coupon. Check the terms before you count on the savings.
- Tax rules on free items vary by place, so the amount at checkout may differ a little.
Frequently asked questions
Is buy one, get one free the same as 50% off?
Yes, if you want both items. You pay for one and get two, so each costs half. If you only want one item, a 50% off sale is much better, because you pay half for just that one.
What is buy 2, get 1 free as a percent off?
It's one third off, or about 33.33%. You pay for 2 items and take home 3, so each item costs two thirds of the regular price.
Is buy one, get one 50% off a good deal?
It's the same as 25% off each of the two items. It's a fair deal if you need two. A 30% off sale on the same items would be cheaper.
How do I compare this with a coupon or a stacked discount?
Work out the coupon price with the discount calculator, which handles two discounts on top of each other. Then enter that combined percent in the comparison box here. To compare several kinds of offers at once, use the deal comparison calculator.
How this calculator is checked
Method: Percent decrease from the regular total to the deal total, spread over every item; straight percent off of the same regular total for the comparison. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-25. Found a problem? Tell us.
Embed this calculator
Put this BOGO Calculator on your own website or blog for free. Paste this code where you want it to appear: