A Loss Calculator helps you quantify a realized decline from your original cost basis to your actual sale proceeds. It is useful when you need a clean dollar amount and a percentage that show how much capital was not recovered after a completed sale. The calculation is intentionally conservative: if the sale price is not below basis, there is no realized loss under this method. That makes the result more reliable for trade review, portfolio reporting, budgeting, and tax discussions.
For accurate results, compare like with like. Keep the currency the same, match the exact quantity sold, and use either gross-to-gross or net-to-net values when fees are involved. If you include purchase commissions in basis, include selling fees in proceeds as well, so the comparison reflects the same accounting treatment on both sides.
How This Calculator Works
The calculator compares the amount you originally invested with the amount you received when the asset was sold. If sale proceeds are lower than cost basis, the difference is a realized loss. If sale proceeds are equal to or higher than basis, the transaction is not a loss in this calculation and the loss amount is treated as zero.
The percent loss is measured against cost basis, not sale price. That matters because the percentage should express how much of the original investment was not recovered. This is why the same dollar loss can produce very different percentages depending on the size of the original position.
Formula
Loss Amount = Cost Basis − Sale Proceeds, only when Sale Proceeds < Cost Basis; otherwise Loss Amount = 0.
Loss Percentage = (Loss Amount ÷ Cost Basis) × 100
Variable definitions:
- Cost Basis: the total amount invested in the sold position, including acquisition costs if you choose to include them.
- Sale Proceeds: the amount actually received from the sale, ideally net of selling fees if the basis also includes fees.
- Loss Amount: the unrecovered portion of the original capital.
- Loss Percentage: the loss expressed as a share of the original cost basis.
| Variable | Meaning | Notes |
|---|---|---|
| Cost Basis | Original invested amount | Use the same quantity and currency as the sale |
| Sale Proceeds | Amount received on exit | Use net or gross consistently with basis |
| Loss Amount | Basis minus proceeds | Set to zero when proceeds are not below basis |
| Loss Percentage | Loss divided by basis | Shows the decline relative to the original investment |
Example Calculation
- Start with a cost basis of 1,200.
- Enter sale proceeds of 900.
- Subtract sale proceeds from cost basis: 1,200 − 900 = 300.
- Divide the loss by cost basis: 300 ÷ 1,200 = 0.25.
- Convert to a percentage: 0.25 × 100 = 25%.
Result: the realized loss is 300 and the loss percentage is 25%.
Where This Calculator Is Commonly Used
- Investment and trading records for stocks, funds, crypto, and other sold assets
- Small business asset disposals where an item was sold below book or purchase cost
- Collectibles, equipment, inventory clearances, and resale transactions
- Tax-preparation notes when you need a clean arithmetic check before classification
- Portfolio reviews where realized downside is tracked alongside realized gains
How to Interpret the Results
The loss amount is the dollar figure that was not recovered. It is most useful for cash-flow review and recordkeeping because it tells you the direct magnitude of the exit. The loss percentage shows severity relative to the original capital, which makes different positions easier to compare.
A low percentage loss may indicate a near break-even exit, while a high percentage loss means a large share of the original basis was not recovered. If the calculator returns zero loss, the sale did not fall below basis under the inputs provided, so you should treat it as break-even or gain rather than loss.
If fees, partial sales, or currency conversion are involved, interpret the result as an arithmetic estimate unless you have already aligned all inputs on the same basis.
Frequently Asked Questions
What is a realized loss?
A realized loss occurs when an asset is actually sold for less than its cost basis. It is different from an unrealized paper decline because the loss has been locked in through a completed transaction. This calculator is designed for realized outcomes, not unsold positions that are merely below purchase price.
Why is loss percentage measured against cost basis?
Cost basis represents the amount originally at risk, so it is the correct denominator for measuring how much of that investment was not recovered. Using sale price would distort the interpretation, because the percentage should describe the decline relative to what you put in, not what you got out.
Should I include fees in the calculation?
Yes, if you want a true net result. The key is consistency: either include fees on both sides or exclude them on both sides. A gross purchase price compared with a net sale price can overstate the loss, while a net basis with gross proceeds can understate it.
What if the sale price is higher than my cost basis?
If proceeds are equal to or greater than basis, there is no realized loss under this method. The calculator should return zero loss, and the transaction should be reviewed as break-even or a gain instead. That keeps the result aligned with standard finance logic.
Can I use this for partial sales?
Yes, but only if the cost basis matches the exact portion sold. Using the full position basis for a partial exit will exaggerate the loss. For accurate partial-sale results, isolate the basis and proceeds tied to the same quantity of shares, units, coins, or items.
Does this calculator handle taxes?
No. It performs the arithmetic for realized loss only. Tax rules can differ based on holding period, jurisdiction, wash-sale treatment, depreciation recapture, and other factors. Use the result as a starting point, then apply the relevant tax rules separately if needed.
FAQ
What is a realized loss?
A realized loss occurs when an asset is actually sold for less than its cost basis. It is different from an unrealized paper decline because the loss has been locked in through a completed transaction. This calculator is designed for realized outcomes, not unsold positions that are merely below purchase price.
Why is loss percentage measured against cost basis?
Cost basis represents the amount originally at risk, so it is the correct denominator for measuring how much of that investment was not recovered. Using sale price would distort the interpretation, because the percentage should describe the decline relative to what you put in, not what you got out.
Should I include fees in the calculation?
Yes, if you want a true net result. The key is consistency: either include fees on both sides or exclude them on both sides. A gross purchase price compared with a net sale price can overstate the loss, while a net basis with gross proceeds can understate it.
What if the sale price is higher than my cost basis?
If proceeds are equal to or greater than basis, there is no realized loss under this method. The calculator should return zero loss, and the transaction should be reviewed as break-even or a gain instead. That keeps the result aligned with standard finance logic.
Can I use this for partial sales?
Yes, but only if the cost basis matches the exact portion sold. Using the full position basis for a partial exit will exaggerate the loss. For accurate partial-sale results, isolate the basis and proceeds tied to the same quantity of shares, units, coins, or items.
Does this calculator handle taxes?
No. It performs the arithmetic for realized loss only. Tax rules can differ based on holding period, jurisdiction, wash-sale treatment, depreciation recapture, and other factors. Use the result as a starting point, then apply the relevant tax rules separately if needed.