While the Thrift Savings Plan generally offers automatic investment for employees–who set up a payroll withholding and then need do little else–one notable exception arises in the “catch-up contributions” aspect.

In the “catch-up” feature, investors who are 50 and older by year’s end may make special investments ($6,000 in 2017, the same as in 2016) toward their accounts over and above the regular annual dollar cap ($18,000 in 2017, also the same as in 2016).

Catch-ups are made through regular payroll withholding, as are standard TSP contributions. The difference is that while standard contributions roll over from one year to the next unless the employee directs otherwise, catch-ups stop at year’s end–regardless of whether the employee has put in the maximum allowable amount up to that time.

Thus, individuals wishing to make catch-up contributions must file a new form TSP-1-C regardless of whether they made catch-ups in the prior year. Also, those who did not make the maximum contribution in one year cannot make up for the difference in the next.