The IRS will eventually send a letter to the taxpayer who used the standard deduction that they must itemize. They may include a bill for tax assuming zero itemized deductions. If that’s what you would have done anyway, you can pay the bill instead of filing an amended return. Or, you can file an amended return to claim whatever itemized deductions you have. You can also amend now, without waiting.
If you wait until after April 15 to amend, on your own or waiting for the IRS notice, you will also pay interest and late payment penalties of about 1% per month of the amount of tax you owe.
