Frequently Asked Questions
Everything you need to know about the Time Dilation Calculator.
What is time dilation?
A prediction of special relativity: a clock moving relative to an observer runs slower than the observer's own clock, by a factor called the Lorentz factor.
What is the Lorentz factor?
γ = 1/√(1 − v²/c²), where v is velocity and c is the speed of light. It's always ≥ 1 and grows sharply as v approaches c.
Why can't I enter a velocity of 1 (the speed of light)?
At v = c, the Lorentz factor becomes infinite, which isn't physically meaningful for objects with mass — only massless particles like photons travel at c.
How much does time dilate for everyday speeds?
Negligibly. Even the ISS's orbital speed (about 7.66 km/s) only dilates time by a few milliseconds per year, which is why the effect is imperceptible in daily life.
What does "elapsed time for the stationary observer" mean?
The time that passes for the observer who is not moving relative to the reference frame, as measured on their own clock.
What is the moving observer's elapsed time?
The proper time experienced by the traveler, found by dividing the stationary observer's elapsed time by the Lorentz factor.
Is this the same as gravitational time dilation?
No, this calculator covers velocity-based (special relativity) time dilation only, not the general relativity effect from gravity.
What are the preset velocities?
Common reference points: the ISS's orbital speed, and fractions of light speed from 0.1c to 0.999c to show how the effect grows.
Is my data stored?
No; all computation happens locally in your browser.
Is it free?
Completely free, no sign-up or limits.