if when you jumped in to the TARDIS it was 1999 then you went back 127 years what year would it be?

Takahiro, if you are travelling in a tardis then you are the time lord. 

And you can travel to whenever and whereever you want. :)

$${\mathtt{1\,999}}{\mathtt{\,-\,}}{\mathtt{127}} = {\mathtt{1\,872}}$$

I wonder as well.... However, it is impossible to travel to the past. But possible to the future.