Final answer:
The maximum net capital loss a taxpayer can deduct in one year is $3,000 for single filers or married filing jointly, or $1,500 if married filing separately.
Step-by-step explanation:
The question asks about the maximum net capital loss that a taxpayer is allowed to deduct in a single year. Each year, U.S. taxpayers can deduct a maximum of $3,000 in net capital losses if they are filing as either single or married filing jointly. If married filing separately, each spouse can deduct a maximum of $1,500.
This means if their losses exceed these amounts in one year, they can carry over the excess to subsequent years to offset capital gains or deduct against ordinary income, up to the annual limit.