{{ summaryHeading }} {{ primaryDisplay }} {{ summaryLine }} {{ dealBadge }} Save {{ money(values.total_savings) }} {{ money(values.final_per_item) }} / item
USD is the display denomination; the calculator does not convert currencies.
$
Use 25 for a 25% discount.
%
Quantity must be a whole number from 1 through 10,000.
items
The neutral default 0% leaves the headline offer unchanged.
%
The neutral default $0 applies no coupon.
$
The neutral default $0 models pickup or free shipping.
$
The neutral default 0% makes a tax-free comparison.
%
The neutral default $0 omits budget-gap guidance.
$
On taxes merchandise after the coupon; off taxes the discounted balance before the coupon.
{{ params.coupon_reduces_taxable ? 'Yes' : 'No' }}
On adds shipping to the taxable base; off keeps delivery outside it.
{{ params.shipping_taxable ? 'Yes' : 'No' }}
Optional; the blank default is calculation-neutral.
Receipt stepAmountChangeMeaningCopy
{{ row.label }}{{ row.amount }}{{ row.change }}{{ row.note }}

What deserves a checkout check?

{{ item.priority }}{{ item.action }}

{{ item.reason }}

ScenarioCheckoutSavedEffective discountDecision useCopy
{{ row.label }}{{ row.total }}{{ row.saved }}{{ row.effective }}{{ row.note }}
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A large sale percentage can shrink once the full checkout is counted. Quantity, a second discount, a flat coupon, shipping, and sales tax all change the amount paid, and they do not necessarily apply to the same base.

Successive percentage discounts multiply. A 20% discount followed by 10% off the reduced balance leaves 72% of the original price, which is a 28% reduction rather than 30%. A flat coupon comes later and cannot reduce merchandise below zero.

Headline discount
The first percentage reduction from the full merchandise subtotal.
Effective discount
Savings against the same full-price checkout after modeled shipping and tax, not just against merchandise.
Taxable base
The merchandise and, where applicable, shipping amount on which sales tax is calculated.

Tax treatment is the most important assumption to verify. Retailer and manufacturer coupons can be treated differently, shipping may or may not be taxable, and rules vary by jurisdiction. The merchant's actual checkout remains authoritative.

A percentage is only meaningful when the reference price is genuine. Comparing final totals across sellers is safer than judging a deal by an advertised markdown from a price that may not reflect a recent ordinary selling price.

How to Use This Tool:

Model one basket at a time using the order in which the merchant applies the offer.

  1. Enter the per-item Original price, Headline discount, and whole-number Quantity.
  2. Add a Stackable discount only if the second percentage is confirmed to apply after the first. Enter the flat coupon separately.
  3. Enter shipping and sales tax, then set whether the coupon reduces taxable merchandise and whether shipping is taxable.
  4. Add a Target checkout when you want an all-in budget comparison. Zero omits the target-gap guidance.
  5. Check Final checkout, unused coupon value, tax base, and scenario comparisons before relying on the advertised rate.

Interpreting Results:

Total savings compares the modeled offer with the same quantity, shipping, tax rate, and shipping-tax choice at full merchandise price. It does not compare against another seller, a historical street price, or a different shipping threshold.

Target gap is positive when checkout exceeds the target and negative when it is under. If a coupon is larger than the remaining merchandise, the unused portion is reported rather than treated as cash or extra savings.

Effective discountDeal labelReading
0%No net discountThe modeled checkout does not beat its same-basket baseline.
> 0% and < 12%Thin dealExtras or a modest offer leave a small net reduction.
≥ 12% and < 25%Balanced dealThe all-in reduction is material but below the strongest band.
≥ 25%Strong dealThe modeled checkout is at least one quarter below its baseline.

Technical Details:

The checkout is evaluated in a fixed sequence. Each percentage is applied to the balance available at that stage, the coupon is capped at remaining merchandise, and tax is calculated from the selected taxable base.

Formula Core:

The merchandise sequence begins with full-price subtotal S, then applies headline rate d, stackable rate k, and coupon C.

S=PQ A=S(1−d100)(1−k100) M=A−min(C,A)

P is original price per item, Q is quantity, A is merchandise after both percentage discounts, and M is merchandise after the coupon.

Tax base B uses either merchandise before or after the coupon, plus shipping only when shipping is taxable. Final checkout then adds shipping and tax.

B=Mtax+Ftax T=Br100 Checkout=M+F+T

F is shipping, r is the sales-tax rate, and T is tax. When the coupon reduces the tax base, Mtax equals merchandise after coupon; otherwise it equals merchandise after the percentage discounts. Taxable shipping contributes F, while non-taxable shipping contributes zero.

The same-basket baseline removes the headline discount, stack, and coupon but keeps quantity, shipping, tax rate, and shipping-tax treatment. Effective discount is the baseline-minus-checkout savings divided by the baseline.

E=Cbase−CofferCbase×100

Rule Core:

RuleExact behavior
Second discountApplied to the already-discounted merchandise balance, not added to the first percentage.
Coupon capApplied coupon is the smaller of coupon value and remaining merchandise; excess is unused.
TargetA positive target gap means the final checkout is over budget.
Extras pressureFlagged when shipping plus tax is at least as large as all applied discounts and coupon savings, provided total savings remains positive.
QuantityMust be a whole number from 1 through 10,000.

Money is held at full numeric precision through the model and rounded for display. USD is the display denomination; no exchange-rate conversion occurs.

Accuracy Notes:

  • Match the merchant's order of operations and eligibility rules. A code that cannot stack should not be entered as stackable.
  • Tax and shipping treatment varies by location, product, seller, and coupon type. Use the actual checkout for a purchase decision.
  • The model does not test whether an original price is a genuine recent selling price or whether a promotion complies with local pricing law.
  • Fixed fees, deposits, credits, rebates, loyalty points, and minimum-spend rules are outside this checkout sequence unless included in the entered amounts.

Worked Examples:

Layered sale with taxable shipping

Two $80 items with 20% off, a 10% stack, a $15 coupon, $8 shipping, and 8.25% tax produce a modeled checkout of about $117.13 when the coupon reduces taxable merchandise and shipping is taxable. The effective reduction against the same $181.86 full-price checkout is about 35.6%.

Coupon larger than merchandise

A 100% merchandise discount leaves nothing for a later $20 coupon to reduce. With $5 non-taxable shipping, checkout is $5 and the full $20 coupon is reported as unused rather than counted as savings.

References: