Part 61: Private - 61.109(k) allows for a maximum of 2.5 hours of training in either an certified flight training device or simulator. If the training is conducted by a part 142 school, then a maximum of 5 hours is allowed. Commercial - 61.129(i) allows for a credit of 50 hours in either a sim or FTD. If the program is conducted by a part 142 school, then 100 hours may be credited.

Part 141: Private - Appendix B to Part 141(4)(c)(2) allows a credit for a maximum of 20 percent of the total flight training hour requirement if the training is in a flight simulator (therefor a 35 hour program - typical - would allow a credit of 7 hours). Appendix B to Part 141(4)(c)(3) allows a credit for a maximum of 15 percent of the total flight training hour requirement if the training is in a flight training device (so a 35 hour program could have 5.25 hours). In the case of a commercial curriculum then it's 30 percent and 20 percent respectively of the total hour requirement of the course (Commercial - Appendix D to Part 141(4)(c)(2) and (3)).

In all cases the flight training can be anything in the curriculum the sim or FTD is certified for, not just instrument flying.