A 15% discount sounds simple until you need to check a price list, invoice, or promotion with several items. Mistakes appear when the percent is applied to the wrong base or rounding is handled differently across lines.
Qsen’s calculator helps you calculate the final price, the savings amount, and the reverse discount when you know the old and new prices.
Direct discount formula
If the original price is 8,000 and the discount is 15%, first calculate the discount amount: 8000 × 15 / 100 = 1200. Then subtract it from the original price: 8000 - 1200 = 6800.
For one item, this is easy. For a larger price list, check a few lines separately to make sure the spreadsheet formula is using the correct base.
Discount and markup are not opposites
A 20% discount followed by a 20% increase does not bring the price back to the original. If 1,000 becomes 800, getting back to 1,000 requires a 25% increase from 800. This mistake is common when planning promotions and returning to regular prices.
When explaining the offer, show both the percentage and the money saved.
Reverse-check the discount
Sometimes you know the old price and the new price. If the old price is 12,500 and the new price is 10,900, the difference is 1,600. Divide by the old price and multiply by 100: 1600 / 12500 × 100 = 12.8%.
This helps confirm whether a promotion matches the advertised discount or whether the number was rounded for marketing.
Common mistakes
- calculating the percent from the new price instead of the old price;
- rounding too early;
- adding multiple discounts together directly;
- forgetting that tax may need a separate check;
- advertising “up to 30%” when a specific item has a smaller reduction.
For a commercial offer, keep the original price, discount percent, savings amount, and final price visible.
Checklist
- the original price is the base;
- the discount amount is calculated separately;
- rounding follows one rule;
- the final price matches the offer;
- savings are shown in money;
- multiple discounts are applied in the right order.
FAQ
Can I multiply the price by 0.85?
Yes. For a 15% discount, 85% of the price remains. Still, calculating the savings amount separately is useful.
How do two discounts work?
Apply them one after another. A 10% discount followed by another 10% discount is not the same as 20% off the original price.
What about invoices?
Use the format required by your invoice template. If tax is involved, check it separately.