Is the check in the mail? If you filed your Form 1040 on time this year, the IRS will tell you in July how big a tax rebate to expect this year. The agency plans to send the actual checks by the end of September. However, your check may be smaller than the advertised $300 for single returns and $600 for joint returns if you owe child support or a debt to a federal agency that puts you in the “tax refund offset” program. Your check may be late if you did not file by April 16 or did not give the Postal Service a change-of-address card. And your check won't arrive at all if you did not owe any tax in 2000. But even taxpayers who miss out on a rebate check will still see a reduction in their withholding beginning in July.