You are standing in a store. One sign says "20% off." Another says "$20 off." A third says "Buy two, get one free." All three are discounts -- but which one is actually saving you the most money? The answer depends on what you are buying, and retailers know exactly how to use that to their advantage.
The Basic Math
Before comparing formats, you need to convert everything to the same unit: actual dollars saved.
To convert percent off to dollars saved: Multiply the original price by the percentage (as a decimal). A 20% discount on a $150 item saves you $150 x 0.20 = $30.
To convert dollars off to a percentage: Divide the discount by the original price, then multiply by 100. A $20 discount on a $150 item is ($20 / $150) x 100 = 13.3%.
In this case, 20% off beats $20 off by $10 on a $150 item. But flip the price, and the answer changes.
When Percent Off Wins
Percentage discounts scale with the price of the item. The more expensive the item, the more a percentage discount is worth in real dollars. On a $500 jacket, 20% off = $100 saved. On a $50 shirt, 20% off = $10 saved. The percentage is the same; the dollar value is very different.
Percent off is almost always the better framing for high-ticket items. Retailers know this, which is why luxury goods, electronics, and furniture sales frequently advertise percentages: "30% off all appliances" sounds better than "$200 off" on a $650 refrigerator (which is only about 30.8% anyway, but the number 200 sounds smaller than 30%).
When Dollars Off Wins
Dollar discounts are fixed regardless of item price. "$20 off any purchase" means more on a $60 item (33% savings) than on a $200 item (10% savings).
Retailers use dollar-off framing strategically on lower-priced items where the percentage would look unimpressive. "$5 off" sounds generous on a $15 item (33% off). If they advertised "33% off," it might actually sound too good and make you suspicious. If they showed "33% off," customers might wonder why the item is priced so high to begin with.
Dollar-off coupons are also common as minimum-spend incentives: "$10 off when you spend $50." These are designed to push you over a spending threshold, often causing you to spend $60 to get $10 off -- a 16.7% discount that required spending more than you planned.
The Breakeven Point
For any percent-off vs dollars-off comparison, there is a breakeven price where both offers are identical in dollar value. You can find it with this formula:
Breakeven price = Dollar discount / Percentage (as decimal)
If the offers are "15% off" vs "$30 off," the breakeven is $30 / 0.15 = $200. Below $200, the $30 off deal saves you more. Above $200, the 15% off deal saves you more. At exactly $200, they are identical.
This is a quick calculation you can do in your head with round numbers. "$25 off vs 20% off" -- breakeven at $25 / 0.20 = $125. Buying something under $125? Take the $25. Buying something over $125? Take the 20%.
Buy X Get One Free: The Real Percentage
"Buy two, get one free" is a percentage discount in disguise. You are buying three items but paying for two, which means you are saving one-third of the total cost. One item free out of three = 33.3% off the total purchase.
"Buy one, get one 50% off" (BOGO 50%) is less generous than it sounds. You pay full price for the first item and half price for the second, meaning you save 25% on the total two-item purchase -- not 50%.
Comparing these to a straight percentage off the whole transaction: a 30% off sale beats a BOGO 50% deal (which is only 25% off your total), and comes close to a true BOGO free deal (33.3%).
Stacking Discounts: The Math Gets Interesting
When you stack a percentage off on top of a sale price, the discounts do not simply add together. A 20% off coupon applied to an item that is already 30% off does not give you 50% off the original price.
Here is how it actually works: Start with a $100 item. Apply 30% off: now $70. Apply 20% off to $70: $70 x 0.80 = $56. Your actual total discount is 44% off the original price, not 50%.
The formula for stacked percentage discounts is: Total discount % = 1 - ((1 - discount 1) x (1 - discount 2)). For 30% and 20%: 1 - (0.70 x 0.80) = 1 - 0.56 = 0.44 = 44% total discount.
Common Retailer Tricks to Watch For
Inflated original prices. A "50% off" deal is meaningless if the original price was marked up 50% before the sale. Always check whether the "original" price reflects what the item actually sold for recently.
Minimum spend requirements. "$10 off $75" requires spending $75 to save $10 -- a 13.3% discount that only applies if you are buying that much anyway.
Per-item vs per-order discounts. "10% off select items" often applies only to specific SKUs with already-thin margins. Check exactly which items qualify before assuming the whole cart is discounted.
Free shipping thresholds. "Free shipping on orders over $35" can push you to spend more to avoid a $5-7 shipping fee. Do the math: spending $35 to avoid a $5 fee saves you 14.3% on the shipping, but if you only needed $25 worth of items, you spent $10 more to save $5.
Quick Reference: How to Compare Any Deal
Step 1: Convert everything to dollar savings on the item you actually want to buy. Step 2: Compare the dollar savings directly. Step 3: Factor in any spending minimums or conditions. Step 4: Pick the deal that saves you the most on what you were already going to buy -- not what makes you spend more to hit a threshold.
The discount calculator does steps 1 and 2 instantly. Plug in the item price and percentage, and you get the exact dollar savings immediately.