This calculator is designed to allow you to determine the time dilation as you approach the speed of light

The interesting things start to happen at 90% the speed of light and as you get very close to the speed of light (99.99999) the numbers go through the roof.

t1 = t / sqrt(1-(v²/c²))  

t1 = time dilation factor
c = speed of light (299792458 meters/sec)
v = velocity (percent of speed of light)