In-service members may elect to invest contributions in the Passport Funds: all members may invest their TDA contributions; Tier I and Tier II members may invest their pension contributions.

For members who invest their contributions in a variable-return Passport Fund, the contributions will purchase a certain number of units, based on the unit value in effect at that time for the Funds. Similarly, when a member reallocates investments out of one of the Funds, units are "sold" or "redeemed" based on the unit value in effect at that time. After transactions are applied to the previous month's total, TRS increases the number of units by .3274% (or 4% annually).