BOGO Calculator

What BOGO costs per item

Buy one get one free is the most misread offer in retail. The sticker says free, and the second item is indeed free, but the deal applies to a pair. Two items for the price of one is a 50% discount on the pair, not a 100% discount on anything.

The number that matters is the price per item after the deal. On a $20 item with BOGO free, you pay $20 for two and each one costs $10. On the same item with BOGO half off, you pay $30 for two and each one costs $15. The first deal is twice as good, and the shelf tag does not always make that obvious.

The calculator shows four figures for any offer: the items you get, the full price you would pay without the deal, the price you pay, and the average cost per item. The last one is the honest comparison, because it is the number you can weigh against the same item sold loose.

It also compares the deal against buying only what you need. That check is what separates a saving from a purchase you would not have made.

BOGO free versus BOGO half off

Most BOGO offers fall into three shapes, and the discount on the pair is always half the discount on the second item. The table below runs each one on a $20 item.

The pattern is worth memorising, because it makes any BOGO offer readable at a glance. A free second item is a 50% discount. A half price second item is a 25% discount. A quarter off the second item is a 12.5% discount. The discount on the pair is always half the headline number.

Retailers lean on this. A shelf tag that reads "buy one get one 50% off" sounds like half off, and it is half off the second item, which lands at 25% for the pair. The price per item column is the one to compare.

Worked example: a $20 buy one get one free offer

Take the default inputs: a $20 item, a buy one get one free offer, one pair, and a shopper who needs one item.

• Items: 2
• Full price without the deal: $40.00
• You pay: $20.00
• You save: $20.00
• Discount on the pair: 50%
• Price per item: $10.00
• Cost of buying only the one you need: $20.00
• Difference: $0.00

That last line is the important one. The shopper pays $20 either way, so the deal delivers a second item at no extra cost rather than a discount on the first. If the second item gets used, the saving is real. If it goes in a cupboard and expires, nothing was saved.

Now switch the offer to half off. You pay $30 for two, or $15 each, and the extra item costs $10 on top of the $20 you would have spent. The deal only pays off if the second item is worth more than $10 to you. Change the quantity to two pairs on the free offer and the numbers scale: four items at $30 each would be $120, you pay $60, and the price per item is $15.

When a BOGO deal is not a saving

A discount on a purchase you would not have made is not a discount. This is the single most expensive mistake in grocery shopping, and BOGO offers are built to trigger it. Three situations turn a BOGO into a loss.

The item expires before you use it. Fresh food, dairy and bakery items are the usual offenders. Two loaves of bread at a 50% discount are not a saving if the second loaf goes mouldy, and the real cost per usable loaf is the full price.

The price was raised for the promotion. A BOGO on an item that costs $12 during the deal and $9 the rest of the year is a worse price per item than the everyday price, and the tag hides it. Compare against what you paid last month, not against the pre-deal tag.

You buy up to qualify. If the deal requires spending $50 to unlock, the money you spend beyond your list is the cost of the discount. A 50% saving on a $20 item is $10, and spending an extra $30 to reach a threshold wipes it out.

The calculator's need field exists for exactly this. Enter what you would have bought anyway, and the difference line tells you whether the deal added cost or removed it.

Unit price, shelf tags and the fine print

The unit price on a shelf tag is the fairest way to compare, and BOGO offers make it harder to read because the tag shows the deal rather than the price per item. Divide the total you pay by the number of items you get, and compare that figure with the unit price of the same product sold loose.

Three lines of fine print change the math. Many BOGO offers require the second item to be of equal or lesser value, so a cheap item paired with an expensive one gives the discount on the cheap one. Some deals apply per transaction rather than per visit, which caps how many pairs you can buy. And some exclude items already on sale, which removes the stacking that makes BOGO genuinely cheap.

Prices also drift, which is why a deal you remember from last year is not the deal in front of you. The Bureau of Labor Statistics price index tracks grocery prices month by month, and the direction has generally been upward, so a BOGO at today's price is not the same as one at last year's.

If a promotion looks misleading, the standard retailers are expected to meet is set out in the FTC's rules on deceptive pricing. Comparing the unit price before and after the deal is the practical test.

How BOGO compares with a straight discount

A straight 50% off one item and a buy one get one free deal sound equivalent and are not. The first gives you one item at half price. The second gives you two items at full price for one, which is the same 50% per item only if you want both.

On a $20 item, 50% off one item costs $10 for one item. BOGO free costs $20 for two items, which is $10 each. The unit price matches, but the cash outlay is double. For a shopper who needs two, the deals are identical. For a shopper who needs one, the straight discount is the better offer because it halves the money leaving the account.

This is why BOGO offers cluster on items people buy in multiples anyway: drinks, snacks, canned goods, cleaning supplies and anything with a long shelf life. The retailer is not being generous, it is increasing the size of a purchase the shopper was going to make.

The honest test is a single question. Would I buy the second item at this price if it were not bundled? If the answer is yes, take the deal. If the answer is no, the straight discount or the single item at full price is cheaper for you, whatever the tag says.