IRS allows FSA/LPFSA users to move up to $610 (up to $570 for 2022) of the previous plan year's contribution into next year's allocation (without counting against the overall contribution limit) to avoid forfeiting money to their employers at year's end.
Your remaining funds from the previous plan year will be rolled over to the FSA/LPFSA from the new plan year AFTER the runout period. The Runout period is an extra time that you can submit manual claims for services rendered in the previous plan year to be reimbursed for that previous plan year's funds.
IRS provides the employer the right to determine the length of the runout period, so this could vary from the company. According to IRS's regulation, the maximum length of the runout period is 90 days.
For example, if your employer provides a 90-day runout period for the FSA plan. At the end of 2022, your FSA balance was $600.
The 90-day runout period is from 1/1/2023 to 3/31/2023. In this period, you can file reimbursement claims for the eligible expenses from 2022 under your 2022.
If you use your Pretax Forma card in this runout period, the expense will use your 2023 funds instead of 2022 funds since the expense happens in the current year.
If you didn't spend any of your $600 in this period, on 4/1, you'll see $570 (IRS rollover limit) rolled over to your 2023 FSA.