The IRS requires employers to report earnings based on the Check Date NOT Pay Period Date. Your last payroll for 2017 includes checks dated 2017, NOT 2018.
If your payroll period ends on Saturday, December 30, 2017 (12/30/2017) or Sunday, December 31, 2017 (12/31/2017), but the checks are dated 2018, this payroll is part of 2018.
BEFORE you Calculate Checks for a payroll with checks dated 2018, you MUST:
1. Verify all special reported earnings are entered in your payroll system
2. Complete the Payroll Calendar Year End Checklist steps:
3. If 12/31/2017 is also your Fiscal Year End, complete the Payroll Fiscal Year End Checklist steps: