Gamma Function

\Delta t' = \frac{\Delta t}{\sqrt{1-v^2/c^2}}

t' = time in the "stationary" frame

t   =  time in the "moving" frame 

v = speed of the moving frame

c = speed of light


Time Dilation

Time dilation:  As seen by an outside observer at rest, time will move more slowly for an object moving close to the speed of light. At the speed of light, time will stop as seen by an outside observer. To an observer moving along with the object all appears normal

Explanation provided by Suite 101

A great website that explains time dilation well is