Discount Calculator

How the Discount Calculator Works

This calculator has two modes for different shopping scenarios:

Single discount mode

Enter the original price and one discount percentage. The formula is:

Sale Price = Original Price × (1 − Discount%)

For example, a $100 item at 20% off:

• Discount amount: $100 × 0.20 = $20
• Sale price: $100 − $20 = $80
• You save: $20 (20%)

Stacked discount mode

When a store offers "20% off + extra 10% off," the discounts are applied sequentially, not added together. This is the key insight most shoppers miss:

• Start: $100
• After 20%: $100 × 0.80 = $80
• After extra 10%: $80 × 0.90 = $72
• Total discount: 28% (not 30%)

Each discount applies to the already-reduced price, which is why stacking always saves less than the sum of the percentages. The calculator handles this math automatically when you switch to Stacked discounts mode.

Quick Reference: Common Discounts

Use this table to estimate sale prices without a calculator. The left column shows the discount percentage; the other columns show what you save and pay on common price points.

The "Multiply by" column is the fastest way to calculate mentally: just multiply the original price by that factor. A $65 shirt at 30% off → $65 × 0.70 = $45.50.

Discount Math You Should Know

Finding the original price from a sale price

If you see a sale price and want to know the original: Original = Sale Price ÷ (1 − Discount%). Example: An item costs $56 after a 30% discount. Original = $56 ÷ 0.70 = $80. This is useful when comparing "was/now" pricing to verify the deal is real.

Comparing "$X off" vs "Y% off"

Stores mix fixed-amount and percentage discounts. To compare them, convert to the same basis:

• $30 off a $120 item → $30 ÷ $120 = 25% discount → final price $90
• 25% off $120 → same thing: $120 × 0.75 = $90
• But on a $60 item: $30 off = $30 final (50% effective), while 25% off = $45 final

Fixed-amount discounts are better on cheaper items. Percentage discounts are better on expensive ones.

The "50% + 50%" trap

A common misconception: "50% off plus another 50% off = free!" That's wrong. Each 50% applies to the remaining price: $100 → $50 → $25. The total discount is 75%, not 100%. This is the most common math error shoppers make with stacked sales.

Worked Examples

Example 1: Black Friday TV

A $799 TV is marked 35% off for Black Friday. You also have a store coupon for an extra 10% off sale prices. What's the final price?

• Original: $799
• After 35%: $799 × 0.65 = $519.35
• After extra 10%: $519.35 × 0.90 = $467.42
• Total savings: $799 − $467.42 = $331.58 (41.5%)

Note: the two discounts (35% + 10%) are not 45% — they're 41.5% because the second discount applies to the already-reduced price.

Example 2: Clearance shoes

Running shoes originally $120 are on a clearance rack with a sign: "Buy one, get the second 50% off." You're buying two pairs. Effective discount?

• Pair 1: $120 (full price)
• Pair 2: $120 × 0.50 = $60
• Total paid: $180 for $240 worth
• Effective discount: ($240 − $180) ÷ $240 = 25% off the pair

This is less than it sounds — "BOGO 50%" is really a 25% discount on the total purchase.

Example 3: Online store with promo code

An online store offers 20% off sitewide. You have a $15-off-$50 promo code. Your cart total is $85. Which is better?

• 20% off: $85 × 0.80 = $68.00 (save $17)
• $15 off: $85 − $15 = $70.00 (save $15)
• 20% off saves you $2 more — use the percentage code.

Rule of thumb: on orders over $75, percentage discounts usually beat fixed-amount coupons. On smaller orders, fixed-amount wins.

Smart Shopping Tips

• Always calculate the final price. Don't compare discount percentages — compare what you actually pay. A 20% discount on a $500 item ($400) is a better deal than 50% off a $50 item ($25), even though the percentage looks smaller.
• Watch for markup before markdown. Some stores inflate prices before a sale. A "50% off" item might be the same price it was last month. Check price history or compare with other retailers.
• Stacked discounts are rarely additive. "40% off + extra 20% off" sounds like 60% off, but it's actually 52%. Use this calculator to see the real savings before you buy.
• Check return policies on sale items. Some stores sell discounted items as "final sale" — no returns. Make sure the item fits and works before leaving the store.
• Calculate price-per-unit. A 30% discount on brand-name cereal might still be more expensive per ounce than the store brand at full price. Always compare unit prices, not just discount percentages.
• Time your purchases. End-of-season sales (January for winter, July for summer) typically offer the deepest discounts. Black Friday/Cyber Monday are good for electronics. Back-to-school season (August) is best for clothing and supplies.