heywhey, this is the equation I was probably thinking of:
That's the actual equations to calculate how time dilation works.
t = time on the stationary frame (usually Earth)
t' = time on the moving frame (space ship, but remember, movement is relative!)
v = velocity
c = speed of light
As you can see, if v is small relative to c (and almost everything is pretty small relative to the speed of light) then there is barely any time dilation at all. But if you crank up v to say 0.6c, then you start getting pretty big discrepencies in measuring time. Also, you cannot get a negative there (since you would be trying to square root a negative number, AND you have to be going faster than the speed of light lol).
Take a look at this website, seems basic but interesting: