Some 2018 federal refunds will be delayed due to the PATH Act
The Protecting Americans from Tax Hikes Act (aka "PATH Act") prevents the IRS from issuing early refunds on any tax return claiming the Earned Income Tax Credit (EIC) and/or Additional Child Tax Credit.
Because identity thieves frequently claim one or both of these refundable tax credits, this measure gives the IRS extra time to detect fraudulently-filed returns, which in turn helps identity theft victims get their legitimate refunds more quickly.
The IRS began issuing tax refunds on returns with the EIC or Additional Child Tax Credit on February 27, 2019.
If your return contains either of these credits, you can track its status at the IRS Where's My Refund? site.