Time Dilation Calculator

This calculator works out relativistic time dilation, how time stretches for an object moving at a large fraction of the speed of light, using Einstein's special relativity. One of the most startling results of relativity is that time is not absolute: a clock moving at high speed relative to you ticks more slowly than your own. The effect is captured by the Lorentz factor, which depends on the speed as a fraction of the speed of light. At everyday speeds it is utterly negligible, which is why we never notice it, but as the speed approaches that of light the factor grows without limit, and time dilation becomes dramatic. This is not mere theory: it is measured daily in particle accelerators, where short-lived particles last far longer when moving fast, and it must be corrected for in the GPS satellites whose clocks would otherwise drift. This tool computes it. You enter a proper time, the time measured in the moving object's own frame, and the velocity as a fraction of the speed of light, and the calculator returns the dilated time observed from the stationary frame, the Lorentz factor, the velocity, and the length contraction factor, which is its inverse. The results update as you type. Use it for physics study, for understanding special relativity, or out of curiosity about the nature of time. The dilated time is the proper time multiplied by the Lorentz factor, one divided by the square root of one minus the velocity fraction squared. At 80 percent of light speed the factor is about 1.67, so a second in the moving frame stretches to 1.67 seconds observed. As the velocity approaches the speed of light the factor heads toward infinity, which is one reason no massive object can reach it. Lengths, meanwhile, contract by the same factor along the direction of motion.

Calculate.co.nz is proud to be partnered with Premium Homes, a recognised leader in eco-friendly, sustainable, and energy-efficient homebuilding. With a dedicated team and award-winning experience, they create homes that prioritise health, comfort, and long-term performance. Their founders, Andrew and Kelly, set out to raise the standard of residential construction in New Zealand by combining practical building expertise with a clear commitment to doing things better for homeowners.

Dilated time = proper time x Lorentz factor, where the factor = 1 / sqrt(1 - (v/c)²). Enter velocity as a fraction of c (0 to 1). Length contracts by the inverse factor.