3000, 我同学一直在做，很多年了，输太多了

You can deduct up to $3,000 annually ($1,500 if married filing separately) from other income for net capital losses after offsetting gains, carrying any excess loss forward indefinitely to future years to reduce gains or up to $3,000 of ordinary income

. This process, called tax-loss harvesting, uses losses from stock sales (and other investments) to lower your overall tax bill by reducing taxable capital gains and ordinary income, but you must avoid wash sales (buying substantially identical securities within 30 days) to claim the loss.