If you are still waiting for a federal tax refund and have not received a CP05 notice from the IRS, it makes sense to check the status of your return. IRS sends notice CP05 when they are reviewing a tax return to verify:
The income reported
The income tax withholding amounts
The claims for tax credits
The withholding claimed on your Social Security benefits
The household help
The Schedule C income
In this case IRS will holding your refund until they finish your review and there is nothing you can do to speed up the process. If you have not received this notice, check the status of your return online at “Where’s My Refund?” page.