The process starts with netting the gain and loss within both short-term and long-term categories. This will result in one of the following six scenarios:

  1. Both short-term and long-term gain.
  2. Both short-term and long-term loss.
  3. Short-term gain and long-term loss, with the gain being greater than the loss.
  4. Short-term gain and long-term loss, with the loss being greater than the gain.
  5. Short-term loss and long-term gain, with the gain being greater than the loss.
  6. Short-term loss and long-term gain, with the loss being greater than the gain.

As shown in the picture below:

 Pay both S&L           Offset S gain               Offset L gain
 capital gain           with L loss                 with S loss
                        pay S gain                  pay L gain
      L
      ┌┐                     S                             L
      ││                     ┌┐
      ││                     ││                            ┌┐
   S  ││                     ││                            ││
   ┌┐ ││                     ││           S                ││
   ││ ││                     ││           ┌┐               ┼┼ offset
   ││ ││                     ││           ││               ││            L
   ││ ││                     ┼┼ offset    ││               ││            ┌┐
   ││ ││                     ││           ││               ││            ││
   ││ ││                     ││           ││               ││            ││
   ││1││          2          ││3          ││4            5 ││          6 ││
───┴┴─┴┴────┼───┬┬─┬┬───┼────┴┴─┬┬───┼────┴┴─┬┬───┼────┬┬──┴┴───┼────┬┬──┴┴───
                ││ ││           ││           ││        ││            ││
                ││ ││           ││           ││        ││            ││
                ││ ││           ││           ││        ││            ││
                ││ ││           └┘           ││        ││            ┼┼ offset
                ││ ││           L            ││        └┘            ││
                ││ └┘                        ┼┼ offset  S            ││
                ││ L                         ││                      ││
                ││                           ││                      ││
                └┘                           └┘                      └┘
                S                            L                       S

            Take loss                 Offset S gain             Offset L gain
            up to 1.5k/3k             to 0, take loss           to 0, take loss
            from S then L             up to 1.5k/3k             up to 1.5k/3k
            carryover rest            carryover rest            carryover rest

  • For the first scenario where you you have gains in both short-term and long-term, you pay the short-term gain at the marginal rate, and the long-term gain at 0-20% or the marginal rate, whichever is less, as explained here.

  • In the second scenario where both short-term and long-term losses are present, you can take your losses up to $1,500 if you are married but filing separately or $3,000. You first take the loss from the short-term then the long-term until the maxium is reached. The loss taken, whether from short-term or long-term, reduces your tax liability by offsetting against your ordinary income at your marginal rate. Any loss exceeding these limits can be carried over to the subsequent year. If not fully absorbed in that year, it will continue to be carried over to succeeding years, and so on, until the year when you retire from life.

  • If you have a net loss in one category and net gain in the other, use the loss to offset the gain until one of the categories reaches zero. After that, you either pay tax on the gain or take the loss in the remaining category.

Capital loss treatments vary by state. For instance, California and Virginia generally conform to federal tax law, but New Jersey neither allows negative income nor any carryovers. Massachusetts, on the other hand, does not permit negative income but does allow both short-term and long-term losses, in that order, to offset up to $2,000 of interest and dividend income, with any excess being carried over to the subsequent year.