I understated my loss carryover by $3000 in 2022. Can I simply correct it in a subsequent year or do I have to go back and do a corrected retrun for each year since then?

If you entered a capital loss carryover of $15,000 on your 2022 Schedule D when it should have been $18,000, and you've been carrying forward the incorrect amount, you generally need to correct this mistake to ensure your future returns are accurate. To fix this, you should amend your 2022 tax return to reflect the correct carryover amount of $18,000. This will adjust the carryover amounts for subsequent years. You may also need to amend your 2023 and 2024 returns if the incorrect carryover affected those years as well. Once you've amended the previous returns, you can then carry forward the correct amount to your 2025 Schedule D. This ensures that your tax filings accurately reflect your capital loss carryovers and that you receive the correct tax benefit. Remember, when amending returns, use Form 1040-X for each year that needs correction.