At everyday speeds the effect is tiny, but GPS satellites must correct for it, and at near light speed it becomes dramatic.
How to use the Time Dilation Calculator
- Speed as fraction of light speed
- Time for the traveller
Results update as you type, and every field accepts the units shown in its menu.
How it works
The Lorentz factor multiplies the moving clock’s elapsed time to give the time measured by a stationary observer.
Inputs explained
| Field | What to enter |
|---|---|
| Speed as fraction of light speed | A number |
| Time for the traveller | Units: years, days, hours |
What each result means
- Lorentz factor γ = 1÷sqrt(1 – [Speed as fraction of light speed]^2)
- Time for a stationary observer = [Lorentz factor γ] × [Time for the traveller]
- Length contraction = 1÷[Lorentz factor γ] × 100
Formula
γ = 1 ÷ √(1 − v² ÷ c²)Δt = γ × Δt₀Worked example
Inputs — Speed as fraction of light speed: 0.9; Time for the traveller: 1 years.
Results — Lorentz factor γ = 2.294157; Time for a stationary observer = 2.2942 years; Length contraction = 43.589 % of rest length.
Frequently asked questions
Is time dilation real?
Yes, it has been measured with atomic clocks on aircraft and in particle accelerators.
Why can nothing reach light speed?
γ becomes infinite, requiring infinite energy.
What formula does the Time Dilation Calculator use?
γ = 1 ÷ √(1 − v² ÷ c²).