Calculator
Example Data Table
| Unit price | Qty | Discount stack | Shipping | Tax | Final payable (expected) |
|---|---|---|---|---|---|
| $120.00 | 2 | 10% order → $5 per item | $8.00 | 7.5% (after discounts, on shipping) | $230.05 |
Formula Used
Start with the subtotal: S₀ = unit_price × quantity. Discounts are applied sequentially to the running total.
- Percent discount: dᵢ = Sᵢ₋₁ × (pᵢ / 100)
- Fixed discount: dᵢ = aᵢ (or aᵢ × quantity if per-item)
- Caps/floors: dᵢ is limited by per-discount caps, overall caps, and minimum payable.
- Update: Sᵢ = max(min_payable, Sᵢ₋₁ − dᵢ)
- Shipping: S = S + shipping
- Tax: tax = base × (tax_rate / 100), then Total = S + tax
If step rounding is enabled, the running total is rounded after each row.
How to Use This Calculator
- Enter unit price, quantity, shipping, and tax rate.
- Choose tax timing and whether tax applies to shipping.
- Add discounts in the exact order they are applied.
- Pick percent or fixed, then choose order or per-item.
- Optional: set caps, minimum-after, or overall discount caps.
- Click Calculate to see the full breakdown.
- Use CSV or PDF buttons to export the results.
FAQs
1) What are stacked discounts?
They are multiple promotions applied one after another. Each discount uses the current reduced total, not the original subtotal, unless your store rules say otherwise.
2) Why is “10% then 10%” not the same as 20%?
The second 10% applies to a smaller base after the first discount. Two 10% discounts equal an effective 19% discount on the original subtotal.
3) When should I use per-item fixed discounts?
Use per-item fixed discounts for offers like “$5 off each unit.” The calculator multiplies the fixed amount by quantity, then applies caps and floors if provided.
4) What do caps and “min after” do?
A cap limits how large a single discount can be. “Min after” ensures the running total never goes below a chosen value after that specific discount step.
5) How does the overall discount cap work?
It limits the sum of all discounts. If the next discount would exceed the cap, the calculator reduces that discount so the cap is not crossed.
6) Should tax be calculated before or after discounts?
Most checkouts calculate tax after discounts, based on the discounted amount. Some setups estimate tax on the original subtotal, so the calculator includes both options.
7) What is step rounding?
Some platforms round after each discount line item. Turning on step rounding imitates that behavior, which can slightly change the final payable versus rounding only at the end.
8) Are the CSV and PDF exports identical?
They contain the same calculation details. CSV is best for spreadsheets, while PDF is a neat snapshot for sharing with teammates or attaching to documentation.