In the year 2000 I purchased stock which was later liquidated due to the company being sold in 2010 at a loss. For some reason I never claimed the the loss in 2010. Can I claim this loss on my 2013 filing or do I need to amend my 2010 return or neither?

you will use a Form 1040X and sch D/ form 8949 I guess which is used to calculate capital gain or loss. If this change to your income changes any other form or schedule that was part of your original filing, you would need to amend those forms as well.If you owned the stock for more than one year any gain or loss would be long term. It owned one year or less it would be short term.The IRS allows you to claim only $3K of losses,$1,500 if married filing separately. on capital assets per year. This amount will reduce your agi/taxable income and taxes. However, if you hav more than $3K of capital losses in a year, you are able to carry the loss forward indefinitely. This allows you to take the loss in future years. When you figure the amount of any capital loss carryover to the next year, you must take the current year's allowable deduction into account, whether or not you claimed it and whether or not you filed a return for the current year.

i mean you need to file amended return for 2010 only if you had long term capital gain offsetting your ltcl in 2010. if not you can't file 1040x and need to carry over ltcl o, sYou are allowed to carry over the unused loss to the next tax year indefinitely.