Why doesn't "20% + 10%" equal "30% off"?
This is a very common mistake: the second discount applies to the price after the first discount, not to the original price. The actual combined discount is 1 − (1−0.20)×(1−0.10) = only 28%, not 30%. This calculator computes and shows the real percentage whenever you enter an additional discount.
The reverse mode ("I only know the final price") is useful if you saw an ad saying "Now SAR 150 after a 25% discount" and want to know the original price before the discount.
FAQ
How do I correctly calculate a stacked discount?
Multiply the discount factors together instead of adding them: (1 − first rate) × (1 − second rate), then subtract the result from 1 to find the true combined discount percentage.
Does this calculator include VAT?
No, this calculator focuses only on the discount. To add VAT to the price after the discount, use the "VAT" calculator on the final result.
Source
General mathematical convention for calculating stacked percentage discounts.
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Last updated: July 2026
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