There are 27 pay periods (vs. 26) in 2018 and the deferral limit has increased. What is not so clear is the impact of this. Changes to TSP to start the new payroll year are required by 12/9 in order to be effective in Pay Period 1. If you simply divide the deferral limit by 26 as in years past, you may not have a contribution in the final pay period, and would not receive an Agency Matching Contribution. See below:
Matching contributions stop if you reach the elective deferral limit before the end of the calendar year so we encourage you to carefully consider your income, budget and contribution election to maximize your benefit.
NOTE: The start of the calendar year (1/1/18) is in the middle of a pay period. To evenly distribute your contributions over the 2018 calendar year; you should make your TSP election between November 26th and December 9th. This election will be effective December 10th (start of pay period 1) and will be reflected in the first pay date of 2018 (January 2nd).
Please do your own research. If you have any questions I would defer to online references or encourage you to call the Benefits Operations Center with questions.