The rules on deducting capital losses are pretty strict. You can deduct capital losses against capital gains. Capital losses can also be deducted against $3,000 of your ordinary income per year. So if you have only ordinary income, no capital gains, and a $30,000 capital loss, it would take you 10 years to fully deduct the capital loss.
If you have such large capital losses, you should review your stocks to see if any have appreciated in value. You can then sell the appreciated stock and generate capital gains. These capital gains will be sheltered by the capital losses. You can then repurchase the stock and obtain a a higher tax basis that reflects its current price.