A good stock market year which brings you a big capital gain, and that’s the flat tax of 31.4% which falls on your earnings since the increase on January 1, 2026. For 12,000 euros of capital gain, this represents 3,768 euros of tax to pay. Except that there is a legal mechanism that allows you to simply erase this bill: use the losses you suffered on the stock market over the previous ten years. A bad year then turns into a tax credit that can be used for a decade.
The principle is simple: if you sold securities at a loss in a securities account over the last ten years, these capital losses can be stored and deducted from your capital gains of the following years. For 10,000 euros of gains made in 2025, 10,000 euros of capital losses carried forward cancel the entire tax. But be careful, this mechanism is not automatic: you must first have scrupulously declared these losses each year via the correct form: the 2074–CMV, and more precisely its annex 2074-CMV.
The form not to be forgotten
Sébastien Defrance, CEO of DeclarAid, a platform specializing in helping investors with tax declarations, is used to this: “When we makes gains or losses on the stock market, each year, we add up the capital gains and losses. If there are more capital losses than capital gains, in a bad year for example, it is a negative figure to report on the tax form. » The mechanism then kicks in: “This loss of value, we will be able to store it. Every year, we will redo the calculation, it can stay up to 10 years if no capital gain arrives”.
Even if you don’t sell any shares the following year, you must continue to report this negative balance on your return. This is the mechanism of “tax stock” : your loss waits in a corner of the declaration until you make a capital gain to be applied against it and reduce your tax. “The year in which you make a capital gain, the capital loss from previous years will be able to compensate for this added value. If it allows it to be completely compensated, you will not pay any tax on your investments this year. And if there are still capital losses, we will be able to continue to use this stock in the following years”details Sébastien Defrance.
Life insurance, PEA: separate rules
Be careful, however: not all investment envelopes work the same way. “ The rules are different for each envelope. On life insurance, this is excluded, it has its own taxation. We cannot carry forward capital losses from the PER, PEE or PEAC either”specifies Sébastien Defrance. For these envelopes, any losses do not generate a tax credit that can be reused elsewhere. This is due to the fact that they already benefit from advantageous taxation (partial exemptions, reductions, etc.) which replaces the traditional capital gains regime.
THE PEA acts as a special caseand the rule is tricky for those who ignore it. The CEO of DeclarAid recalls that “the PEA allows you not to pay taxes after 5 years”. “There are therefore two scenarios: if we withdraw from the plan before these five years, there is an automatic closure of the PEA, and the possibility of carrying forward the capital loss”. But if the PEA is more than five years old and it is still at a loss, it becomes complicated. In the event of partial withdrawals, we cannot carry forward any capital losses. For this to be possible, you must sell all your lines and close the plan to note the overall loss in value.
What to do if you forgot to carry forward your capital losses from recent years? “In case we forget, there is no official text on the subject. The best would then be to contact your tax center via secure messaging to try to make up for this loss of value”recommends Sébastien Defrance. There is a second trap that we should not fall into: that of using our most recent capital losses as a priority. However, the losses have an expiration date of ten years, and for this year’s declaration (2025 income), a capital loss realized in 2015 is the last one still available. Beyond that, it disappears.
