The formula
How to calculate stock loss
A loss and the recovery it demands are not the same size. Falling 35% requires a 54% gain to get back to where you started, and that asymmetry is the most important thing this calculator shows.
The gap widens sharply as losses deepen: down 20% needs 25% back, down 50% needs 100%, down 80% needs 400%. The arithmetic is unforgiving because the gain is calculated on the smaller base that remains.
Fill in the following:
- Buy price per share
- Current price per share
- Number of shares
Results appear immediately — there is nothing to submit. Changing a field rewrites the link, so you can share the exact scenario you are looking at.
Worked example
Here is the calculation with the starting values:
- Buy price per share: 40
- Current price per share: 26
- Number of shares: 300
That gives:
- Loss: 4,200
- Loss: 35 %
- Gain needed to break even: 53.85 %
Reading the result
Use the recovery figure as a reality check, not as a reason to hold. The market has no memory of your purchase price — the only question that matters is whether you would buy this holding today at this price.
Where this goes wrong. Averaging down to lower the break-even price. It works arithmetically and often fails in practice, because it concentrates more money in the position that is already going wrong.
In the UK, realised capital losses can be set against capital gains in the same year, and carried forward indefinitely if reported to HMRC in time. The loss has to be crystallised by selling — an unrealised loss does nothing.
Selling to bank a loss and buying the same share back within 30 days causes the disposal to be matched against the repurchase for capital gains purposes, which cancels the loss. It exists specifically to prevent that manoeuvre.
The headline figure is loss. With 40 buy price per share, 26 current price per share and 300 number of shares, that comes to 4,200. Change any field and the figure moves with it.