Working 01 · The amount and its units
An oath research discount, written as subtraction.
The useful number is the dollar reduction on the merchandise eligible for a code. Once you know that starting amount, the arithmetic takes two steps: multiply to find the saving, then subtract to find the merchandise remaining.
Give the percentage a dollar base.
Let S mean the eligible merchandise subtotal in US dollars. Keep tax and freight out of S. It’s the amount the percentage applies to, which may need checking against the shop’s displayed discount calculation. A grand total with postage already added gives you a different starting point.
Saving = S × percentage ÷ 100
S is dollars. The percentage divided by 100 is a fraction. Multiplying them produces dollars again.
Work through the $120 illustration.
GRANT takes 20% off for new customers on their first order only. On our hypothetical eligible subtotal, multiplying $120 by 0.2 gives $24. That’s the saving on merchandise.
$120 × 0.2 = $24
$120 − $24 = $96
The first answer is the saving; the second is merchandise remaining.
For the same $120 base, GRANT15 takes 15% off, saving $18 and leaving $102. It’s for everyone. There’s no minimum, and it applies to repeat orders. Start from $120 again for this alternative. Don’t apply it to the first line’s remaining amount; combining the codes is unconfirmed.
Read “remaining” carefully.
The result is still a merchandise amount. It doesn’t include tax, freight or a decision about the shipping threshold. Those lines belong to checkout. The live worksheet keeps both alternatives on screen so you can compare equal starting amounts.
The worksheet rounds the saving to the nearest cent, with half a cent rounded upward. It then subtracts that rounded saving from your starting amount. Checkout may round differently. If the figures differ by a cent, compare the eligible subtotal and the displayed discount before paying.
These are examples of arithmetic, with no product price attached. Oath Research sells research-use-only material. Its homepage on October 19, 2026 said an account is required to browse the catalog. Use your account’s eligible subtotal when comparing a real basket, then read it against the checkout result.