Carryover from 2015 is -17,130. Why does it change that number on the form to -14,130 and then deduct the $3318 (this year's loss + capital gain) leaving only $10,812.

[TomYoung · Accepted solution]

Mechanically what you describe is how capital gains and losses work.

All capital gains and losses arising from any and all sources are netted against one another.  If the result is a capital loss then $3,000 of that remaining loss can be used against "ordinary" income, and that appears to be exactly what happened.

($17,130) Loss carried over
   $3,318  "This years" net capital gain
   $3,000  Amount applied to ordinary income
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($10,812) Loss carried over

Tom Young