The base year for FASA is the year 2254. I don't know why this is, but maybe it's because this is the earliest date in which a TOS episode takes place, and that would be "The Cage". It is also about 100 years after the founding of the UFP. Here's what you do: In a FASA date like 2/1706 only the first two numbers after the "/" are important. In this case, it's 17 and so you add 17 years to 2254 to give you 2271. The last two numbers are the month, and the first number before the "/" is the century. 1 means the first century of the UFP, 2 means the second century of the UFP. In a date like 1/8801, you would have to subtract 12 from 2254, which gives you 2242.
FASA makes some assumptions about TOS dates and screws up at times, but using the base year I mentioned will get you by nicely.