Re: TaxCaster How do I enter a negative number representing a LT Capital Loss? I unsuccessfully tried (-5000) without and results. Thank you.

The Max net  cap loss that can be deducted on the form 1040 is $3000 after all cap gains have been covered.  I was able to enter -10K without issue in Taxcaster and it worked just fine  because you don't get to deduct it all due to the cap. 

Enter the long-term capital loss with the minus sign, but without the parentheses.

In addition to the accurate information in the posts by @Critter and @rjs, also note that the short-term gains/losses screen comes up prior to the long-term capital gains screen. 

If you should happen to enter a loss of $3,000 or more (e.g., $-3000) in the short-term gains/losses screen, then whatever loss you enter in the long-term gains/losses screen will have absolutely no impact.