A capital loss is the difference between the adjusted basis (the amount you paid) of an asset and the amount you received when you sold it. If total capital losses are greater than the total capital gains, then you have a net capital loss. If the net capital loss is greater than the amount you can deduct in the current tax year, you have a capital loss carryover.
If your net capital loss is more than the limit (up to the amount of your capital gains plus $3,000, or $1,500 if married filing a separate return), you can carry the loss forward to later years.
To find out if you have a capital loss carryover, refer to your 2016 Form 1040 Schedule D, Part III, Lines 16 and 21. If line 21 shows a loss and that loss is less than the amount shown on line 16, or the amount on your 2016 Form 1040, line 41 (or your 2016 Form 1040NR, line 39, if applicable) is less than zero, you have a capital loss carryover. You can use the Capital Loss Carryover Worksheet found in Publication 550, Investment Income and Expenses, or in the Form 1040, Schedule D Instructions, to figure the amount you can carry forward.