How it works
This calculator tackles a specific retail puzzle: you're staring at a price tag showing what you'll pay at the register, you know the promotional percentage that was applied, and you want to reconstruct what the merchandise cost before the retailer marked it down. That backward direction matters when comparison shopping, verifying whether a "doorbuster" actually represents meaningful savings, or budgeting for repeat purchases at regular pricing.
Shoppers encounter this constantly. A sweater rings up $60 with a 25% markdown advertised — but was it originally $80? $85? The sticker only shows today's cost. Big-box electronics stores, outlet malls, and online flash-sale platforms all display the reduced figure prominently while burying or omitting the starting figure. Without recovering it, you can't judge whether this promotion beats a competitor's everyday pricing or whether waiting for a deeper cut makes sense.
The tool also handles the forward case — plug in a known starting figure and discount rate to see what you'll owe. But its distinctive strength is the reverse path, and that's where most people get tripped up doing mental arithmetic.
The formula
Original Price = Sale Price ÷ (1 − Percent Off ÷ 100)
Worked example
Say you're holding a pair of boots marked $60, signage says 25% off, and you want to know the pre-sale figure. This is the backward scenario — sale price known, original unknown.
Percent as decimal: 25 ÷ 100 = 0.25
Remaining fraction: 1 − 0.25 = 0.75
Original Price: 60 ÷ 0.75 = 80
The boots carried an $80 tag before the markdown took effect.
A quick sanity check on that result:
Discount amount: 80 × 0.25 = 20
Sale Price: 80 − 20 = 60
That confirms the $60 figure on the sticker matches a 25% reduction from $80.
Common mistakes
The single biggest error is dividing the sale price by the discount percentage itself — calculating 60 ÷ 0.25 = 240 and concluding the boots originally cost $240. That answer is nonsensical because the markdown removed 25% of the original, not 25% of today's price. The $60 you pay represents the 75% that remains, so you divide by 0.75, not 0.25.
Another trap: subtracting the percentage from the sale price rather than reversing through it. Taking $60 and adding 25% back ($60 × 1.25 = $75) undershoots because the 25% you're adding is calculated on the wrong base — the smaller, post-cut figure instead of the larger pre-cut one.
| Scenario | Wrong move | Right move | Result |
|---|---|---|---|
| 25% off, sale $60 | 60 ÷ 0.25 | 60 ÷ 0.75 | $80 original |
| 25% off, sale $60 | 60 × 1.25 | 60 ÷ 0.75 | $80 original |
| 40% off, sale $54 | 54 ÷ 0.40 | 54 ÷ 0.60 | $90 original |
| 40% off, sale $54 | 54 × 1.40 | 54 ÷ 0.60 | $90 original |
One more wrinkle: stacked promotions. When a store advertises "25% off plus an extra 15% at checkout," those reductions compound sequentially — multiply by 0.75, then by 0.85 — rather than adding to 40% off. The combined effect (0.75 × 0.85 = 0.6375, equivalent to 36.25% off) is always less generous than the simple sum suggests.
This tool produces an estimate for personal budgeting and price comparison, not professional pricing or audit guidance.