Black Friday Savings Calculator
Check whether a Black Friday deal is a genuine saving against the normal price.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
Retailers sometimes raise prices in the weeks before a sale so the discount looks bigger, which is why comparing against the lowest recent price matters more than comparing against the list price. A claimed 40 percent off is meaningless if the item is 10 percent more than it was in September.
Worked example
calculated with the default values below
Deal price 299 $ · Listed original price 499 $ · Lowest price in the last 3 months 379 $ · Average price over the year 420 $ · Do you actually need it Would be nice to have Claimed discount off list price 40.1 % · Real discount vs recent low 21.1 % · Saving vs the yearly average 121.00 $ · Is it a real deal? Yes — cheaper than it has been recently · Advice Only a real deal if it is replacing something you already planned to buy
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
D = (1 − deal/ref) × 100
- deal
- Deal price
- ref
- Reference price (listed or recent low)
- D
- Discount percent (can be negative)
Verdict vs the recent low: real deal above +5%, marginal from −2% to +5%, otherwise not a deal; saving vs average = average − deal.
Frequently asked questions
Why does the real discount use the recent low not the list price?
Claimed discount off list price is 1 minus deal over listed, here about 40 percent, but retailers often inflate the list price beforehand, so the tool also computes real discount versus the lowest price in the last three months, about 21 percent at the defaults. The Is it a real deal verdict triggers only when that real discount beats the recent low by more than 5 points; a marginal deal sits within 2 points of it.