Three ways to think about a discount, switched with the buttons at the top. "% off" is the Western style: final price = original × (1 − percent/100), and the saving is original − final. "X-zhé" is the East-Asian style where a factor of 8.5 (八五折) means you pay 85% of the price — final price = original × factor / 10 — a factor of 10 is no discount and 5 is half price. "Find the rate" reverses everything: give the original and the sale price and it returns both the percent off, (original − sale) / original × 100, and the equivalent zhé factor.
Whichever mode you pick, the tool always reports the final price, the money saved and the discount rate so the three numbers stay consistent. Values recalculate live as you type and are rounded to two decimals for display. All calculations run locally in your browser and nothing is uploaded.