⏳Time Dilation Calculator
See how time slows down as you approach the speed of light.
Free Time Dilation Calculator
Our free time dilation calculator applies special relativity's time dilation formula, t′ = t / γ where γ = 1/√(1 − v²/c²), to show how much slower a clock moving at velocity v runs compared to a stationary observer. Enter a velocity as a fraction of the speed of light and an elapsed time, and see the Lorentz factor, the dilated time experienced by the moving observer, and exactly how much time is "lost" between the two frames.
Use the presets to explore everyday and extreme cases — from the International Space Station's orbital speed, where the effect is a tiny fraction of a second per year, to velocities near the speed of light, where a year for a stationary observer can correspond to just weeks or days for the traveler. The effect only becomes noticeable at a meaningful fraction of light speed, which is why we don't experience it in daily life.
Built for physics students studying special relativity, and for anyone curious about how motion affects the passage of time. No sign-up, no downloads — just instant results.
About the Time Dilation Calculator
Features
Lorentz factor
See γ = 1/√(1 − v²/c²) computed precisely for any velocity.
Real-world presets
From the ISS's orbital speed to velocities near light speed.
Adaptive time formatting
Results shown in seconds, minutes, hours, or days as appropriate.
Time-lost readout
See exactly how much time the moving observer "loses" compared to the stationary one.
Frequently Asked Questions
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.