How the Cyber Monday Calculator works
Cyber Monday deals rarely stop at a single percent-off tag. Retailers layer a site-wide sale discount, then let you stack a coupon code on top, then charge sales tax on whatever is left. This calculator applies each step in the same order a real checkout does, so the number you see matches what your card is actually charged.
The formula
Each discount is a multiplier applied to the price remaining after the previous step — discounts stack multiplicatively, not by adding percentages together:
Price after discount = Original price × (1 − discount / 100)
Price after coupon = Price after discount × (1 − coupon / 100)
Order total = Price after coupon × (1 + sales tax / 100) × quantity
Total saved compares the pre-tax discounted price against the pre-tax original price, multiplied by quantity: Saved = (Original price − Price after coupon) × quantity.
Worked example
Take a $199.99 item with a 30% Cyber Monday discount and a 10% coupon, 7% sales tax, buying one unit. The discount brings it to $199.99 × 0.70 = $139.99. The coupon then applies to that discounted price: $139.99 × 0.90 = $125.99. Adding 7% sales tax gives an order total of about $134.81. Total saved versus the $199.99 list price is $74.00, which is a 37.0% discount overall — not the 40% you'd get by simply adding 30% and 10%.
Why stacked discounts don't add up
A 30% discount followed by a 10% coupon leaves 0.70 × 0.90 = 0.63, or 63% of the original price — a 37% total reduction. Adding the percentages (30 + 10 = 40%) overstates the real savings because the coupon is calculated on a smaller, already-discounted balance rather than the full original price. The gap between the "add them up" estimate and the real stacked result grows as either discount gets larger.
Where sales tax fits in
This calculator applies sales tax after both discounts, on the price you actually pay — the standard approach used by most U.S. retailers, since sales tax law generally taxes the transaction amount, not the pre-discount list price. If your state or retailer taxes the pre-discount price instead, your real total will be slightly higher than shown here.