Calculate relativistic time dilation with Δt = Δt₀ / √(1 − v²/c²) — how much time stretches for a fast-moving clock as seen by a stationary observer. Also shows the Lorentz factor γ.
A 57-second animation: light clocks, relative motion, and why 1 second becomes 2.29 at 0.9c.
Special relativity says moving clocks run slow. A time interval Δt₀ measured on a clock moving at speed v appears stretched to Δt = γΔt₀ for a stationary observer, where the Lorentz factor γ = 1/√(1−v²/c²).
At everyday speeds γ ≈ 1 and the effect is negligible, but it grows without limit as v approaches the speed of light. Enter speed in m/s (the speed of light is 2.998×10⁸ m/s); the calculator returns the dilated time and γ.
For the underlying physics, read our explanation of special relativity and time dilation.
Time dilation is the slowing of a clock as observed from a frame in which the clock is moving. The faster it moves, the more its time stretches relative to a stationary observer.
Δt = Δt₀ / √(1 − v²/c²) = γΔt₀, where Δt₀ is the proper time, v the speed and c the speed of light.
γ = 1/√(1−v²/c²). It equals 1 at rest and rises toward infinity as v approaches c. It multiplies the proper time to give the dilated time.
Yes. It is confirmed by fast-moving muons reaching the ground, atomic clocks flown on aircraft, and the corrections GPS satellites must apply to keep accurate time.