How to Calculate a Discount and Then Sales Tax (Why Stacked Discounts Don't Simply Add Up)

Keywords: discount then sales tax, how to calculate stacked discounts, 20% off plus 8% tax, discount before or after tax, percent off calculator

Quick Answer

Discount first, then tax = price × (1 − discount) × (1 + tax rate). Tax first, then discount gives the same result (multiplication order does not matter). Stacked discounts do not add: 20% off then 10% off is 100 → 80 → 72, a 28% saving, not 30%.

Example 1: Discount, Then Tax

Price 100, 20% off, 8% tax:

• After discount: 100 × 0.8 = 80
• Tax: 80 × 8% = 6.40
• You pay: 80 + 6.40 = 86.40

Tax first: 100 × 1.08 = 108, then 108 × 0.8 = 86.40. Same answer.

Check the store's rules: some stores compute tax on the pre-discount price (certain coupon types do this). The receipt decides.

Example 2: Stacked Discounts

Price 200, 20% off, then a 10% coupon:

• After 20%: 200 × 0.8 = 160
• After 10%: 160 × 0.9 = 144
• Total saving: 56, which is 28% of 200

Adding them to 30% gives 200 × 0.7 = 140 — 4 too low.

Example 3: Spend-and-Save vs. Percent Off

"Spend 200, take 30 off", plus 10% off, on a 220 order:

• Spend-and-save first: 220 − 30 = 190, then 10% off = 171
• Percent first: 220 × 0.9 = 198, which no longer reaches 200, so no spend-and-save = 198

The order of rules changes the result — check whether the threshold applies before or after the discount.

Example 4: Several Items

Item	Price	Discount	Tax
A	50	20%	8%
B	30	none	8%

• A: 50 × 0.8 = 40, tax 3.20
• B: 30, tax 2.40
• Total: 40 + 3.20 + 30 + 2.40 = 75.60

Example 5: Adding a Tip

Bill 86.40 including tax, plus 15% tip: 86.40 × 15% = 12.96, total 99.36.

Doing It Step by Step in a List Calculator

CalcList is a calculator that works like a list: one number or formula per row, optional names, and references to other rows with L1, L2, L3. According to its App Store description, "L1 - 20%" and "L1 * 8%" work the way you expect.

That keeps every step visible:

Row	Content	Meaning
L1	100	Price
L2	L1 - 20%	Discounted price
L3	L2 * 8%	Tax

Change L1 and everything below updates live — no "=" button, no retyping. Built-in templates include Discount and Bill Split.

Get CalcList (iPhone and iPad, 17 languages, free with no ads, works offline)

FAQ

Q: Is it better to take the discount before or after tax? A: If tax is a flat rate on the same base, the result is identical. The difference is whether the store taxes the pre- or post-discount price.

Q: Can I just add two discounts together? A: No. Multiply them: (1 − 20%) × (1 − 10%) = 0.72, a 28% saving.

Q: How do I turn "20% off" into a multiplier? A: Multiply by 0.8.

Q: Does CalcList cost money? A: The core is free with unlimited rows and formulas. Pro is a one-time purchase for saved templates and sharing; there is no subscription.

About CalcList

Item	Detail
Full name	CalcList – Smart List Calc
Type	List-style calculator
Platform	iPhone / iPad
Languages	17
Price	Core free, no ads; Pro one-time purchase
Highlights	Row references L1/L2, live results, smart total that never double-counts, built-in templates, offline
Download	App Store

Related: Splitting the Bill Without the Anxiety, CalcList vs. a Traditional Calculator