Combined discount basis review
Compare discounts calculated on the original amount with discounts applied one after another. Keep the agreed method, cent rounding and excluded charges visible before preparing a document.
Free to use · Fictional examples · Local calculationTwo percentage discounts do not identify their calculation basis by themselves. This worksheet shows both methods; choose a method only after checking the actual agreement or source-system record.
Compare two discount methods
AUD amounts, one eligible subtotal and 2–8 percentage discounts only. Enter one rate per line. Use a consistent pre-GST basis; this review neither adds nor determines GST. An excluded charge is added unchanged after discounts.
Confirm the scope, then review the inputs.
Worked case: 10% and 20% are not always 30%
With a fictional eligible subtotal of AUD100 and an excluded AUD5 charge, sequential discounts remove AUD10, then AUD18. The eligible amount becomes AUD72; adding the unchanged charge gives AUD77. On the original-basis method, both discounts use AUD100: AUD10 plus AUD20, leaving AUD70 plus AUD5 = AUD75.
The AUD2 difference is a method difference, not a rounding error. Neither result establishes what the customer agreed. A second fictional eligible subtotal of AUD0.03 with two 10% discounts illustrates rounding: rounding each discount produces AUD0.03 remaining; retaining fractions until the end produces AUD0.02.
Resolve the basis before changing an invoice
Check the accepted price, discount classes, eligible lines, permitted combinations and rounding rule. A product-level discount followed by an order-level discount can use a different base from two order-level percentages. The Shopify help page linked below documents this distinction for its own system. This independent worksheet does not reproduce its eligibility rules, shipping treatment or checkout.
The original-basis calculation applies each entered percentage to the unchanged eligible subtotal. The sequential calculation applies the next rate to the remaining amount. Under per-step rounding, each discount is rounded half up to cents before subtraction. Under final rounding, exact rational arithmetic is retained and only the combined discount is rounded half up. The report shows both policies so a small difference is visible.
Keep excluded amounts and prior documents separate
Use the excluded-charge input only for an amount that every entered discount leaves untouched. It is not automatically a shipping rule. Do not put a discountable delivery charge there merely because it is delivery. Mixed eligibility across several lines, fixed-dollar vouchers, buy-one-get-one offers, refunds and already issued credit adjustments need a separate source review.
The optional recorded final amount is compared with the selected mathematical result. A mismatch does not authorise a correction or prove overcharging. A match does not prove payment, promotion eligibility or correct GST. Rates totalling more than 100% are rejected for the original-basis method; sequential percentages may total more than 100% while each individual rate remains within 0–100%.
Verify before preparing a document
Resolve any method or amount difference in the original records. For a verified new charge, manually enter the agreed descriptions and final amounts in the existing tool. Do not apply the same discounts again to an amount that is already net of them.
Inputs are processed locally, without upload, account storage or invoice-draft writes. Your browser may restore form values; protect your device and keep any copy you need. A downloaded review is working notes, not an invoice, receipt, tax decision or successful invoice export.
Open the original tool for a verified documentStart the original tool without signing in. Free output has branding and usage limits. This review does not automatically create an invoice or submit a payment.
Sources and scope
Shopify’s own help distinguishes calculation order and the original subtotal basis for multiple percentage order discounts. It supplies workflow context, not a universal rule for your agreement or an endorsement of this worksheet.
Sources and fictional examples reviewed 6 November 2026.