Taken off the already-reduced price, like "extra 10% off at checkout." Leave at 0 if there is none.
Final price$57.60
You save$22.40
Total discount28%
Original price$80.00
Price after first discount$64.00
Extra savings from additional discount$6.40

80 × (1 − 0.2) × (1 − 0.1) = $57.60 — a combined 28% off, not 30%, because the second discount applies to the reduced price.

Discount Calculator · free calculator by CalcWorthy