Calculating Loss Percentage: Formula and Examples

Loss percentage shows how large a loss is compared with the original amount, usually the cost price. Enter the cost price and the selling price to calculate the loss as a percentage, along with the amount lost.

Formula

Loss percentage = (loss amount ÷ original amount) × 100. For a sale, the loss amount is the cost price minus the selling price:

Loss percentage = ((cost price − selling price) ÷ cost price) × 100

• Cost price (c): the amount originally paid or otherwise used as the comparison baseline, in dollars in this calculator.
• Selling price (s): the amount received from the sale, in dollars.
• Loss amount (l): cost price minus selling price, in dollars.
• Loss percentage (p): loss amount divided by cost price, multiplied by 100, expressed as a percent.

The formula assumes the selling price is lower than the cost price. A positive result means a loss; zero means the two amounts are equal. If the selling price is higher, the calculation returns a negative percentage, which indicates a gain of that size relative to the cost price—not a loss.

Worked Example

Using the calculator’s default values, the cost price is $100 and the selling price is $80.

1. Find the loss amount: $100 − $80 = $20.
2. Divide the loss by the cost price: $20 ÷ $100 = 0.2.
3. Convert the decimal to a percentage: 0.2 × 100 = 20.00% loss.

The amount lost is $20.00. Both outputs use the same default inputs; the percentage is rounded to two decimal places.

When to Use Loss Percentage

Loss percentage is useful when you want to compare losses across transactions with different original amounts. A $20 loss on an item that cost $100 is 20%, while a $20 loss on one that cost $500 is 4%. The dollar loss is identical, but the percentage provides context relative to the starting cost.

The calculation also applies outside buying and selling when a loss is measured against an original quantity or value. For example, if a container holds 50 liters before a process and 45 liters afterward, the decrease is 5 liters, or 10% of the original 50 liters. Keep the same units for both values; the units cancel during division.

For a fair comparison, decide what counts as the original amount before calculating. In a simple sale, that is usually the purchase cost. If your purpose requires other costs—such as shipping, materials, or transaction expenses—you may need to add those to the cost basis. The basic formula does not include them automatically.

Reading the Result and Choosing a Baseline

The denominator is important: loss percentage is measured against the original amount, not the selling price. In the example, dividing $20 by $80 would produce 25%, but that answers a different question: the loss as a share of the selling price. The standard loss percentage relative to cost is 20%.

• Positive percentage: the selling price is below the cost price, so the result is a loss.
• Zero percentage: selling price equals cost price, so there is no loss or gain on this comparison.
• Negative percentage: selling price exceeds cost price; the magnitude represents the gain percentage relative to cost.

A percentage describes a ratio, not a currency amount. Read “20% loss” together with its baseline: it means the loss equals 20% of the cost price. It does not mean the item lost 20 percentage points, nor that its selling price is 20% of cost; at a 20% loss, the selling price is 80% of cost.

Common Mistakes and Limits

The most common error is dividing by the wrong value. Use the original cost price as the denominator for the standard loss percentage. Another mistake is reversing the subtraction: loss amount is cost price minus selling price. Reversing it changes the sign and can make a loss appear to be a gain.

• Compare like with like: use the same currency and compatible units for both amounts.
• Do not round the loss amount or intermediate ratio too early; round the final percentage for display.
• Check that the cost price is greater than zero. A zero baseline makes the percentage undefined, and negative cost values generally do not fit the ordinary sale example.
• Do not assume the result captures every business cost. The calculation only uses the two values entered.

Whether a sale produced a loss in the broader sense depends on what costs and adjustments belong in the comparison. The formula itself cannot determine those details. It only calculates the percentage from the baseline and final amount supplied.

Related Calculations

Loss amount and loss percentage are related but different. The loss amount is an absolute difference in currency or units; the percentage expresses that difference relative to the original amount. To find a selling price after a known loss percentage, subtract the loss fraction from the original price: selling price = cost price × (1 − loss percentage ÷ 100). For example, a 20% loss on $100 gives $100 × 0.80 = $80.

For a gain, use the same comparison baseline and reverse the difference: gain percentage = ((selling price − cost price) ÷ cost price) × 100. This is not interchangeable with a markup calculated as a share of selling price, sometimes called margin. Always identify the denominator when comparing percentages, because two valid ratios can describe different things.

Frequently Asked Questions

What is the formula for calculating loss percentage?
Subtract the selling price from the cost price, divide the loss by the cost price, and multiply by 100: ((cost price − selling price) ÷ cost price) × 100.

Do I divide the loss by cost price or selling price?
For standard loss percentage, divide by cost price—the original amount. Dividing by selling price gives a different ratio.

Can loss percentage be more than 100%?
With a nonnegative selling price and a positive cost price, the loss cannot exceed 100%: the greatest loss is when the selling price is zero. A result above 100% usually signals an input, sign, or baseline issue, or a situation outside the ordinary sale formula.

What does a negative loss percentage mean?
It means the selling price is above the cost price. The negative sign indicates a gain rather than a loss; its absolute value is the gain percentage relative to cost.

How do I calculate loss percentage if I know the loss amount?
Divide the known loss amount by the original cost price and multiply by 100. For instance, a $15 loss on a $60 cost is ($15 ÷ $60) × 100 = 25%.

Related

• Calculating Absorbance From a Calibration Curve
• Win-Loss Percentage: Formula and How to Calculate It
• Sphere Volume: Formula, Calculation, and Examples

in c | Cost price | $ | 100 | 0
in s | Selling price | $ | 80 | 0
out p | Loss percentage | % | (c - s) / c * 100 | 2
out l | Loss amount | $ | c - s | 2