Offsetting-position rules, at a mechanical level

Two positions that move against each other create a specific problem for any system that counts gains and losses at different moments: the loss can be taken now and the gain left for later.

Offsetting-position rules close that gap by mechanical means. Where two positions substantially reduce each other's risk, a loss realised on one leg is held back to the extent of unrecognised gain remaining in the other. The held-back amount is generally not destroyed; it waits, and it becomes available when the offsetting gain is itself recognised or the offset ends.

The arithmetic is a comparison of two figures. Close the offsetting leg at a loss of $138,400 while the position it offsets carries $151,900 of unrecognised gain, and the whole loss is held back, because $138,400 does not exceed $151,900. Change the unrecognised gain to $46,000 and $46,000 of the loss is held back while $138,400 − $46,000 = $92,400 becomes available. The loss did not change at all. The other side of the pair did.

A second mechanic often travels with the first. Interest and carrying costs attributable to an offsetting position may be added to the basis of the position rather than relieved in the period, so a cost that would otherwise reduce income this year instead reduces a gain at some unknown future date. Treat $9,250 of carrying cost that way and it is not lost, but it has moved to a different year and a different category.

Systems differ on the definition of substantially reduced risk, on which instruments are within scope, and on what identification or record-keeping is required. The mechanism is general; the treatment is not, and the difference belongs with a qualified adviser.