Time Dilation Calculator
Time dilation is one of the most remarkable predictions of Einstein's special relativity: time passes more slowly for objects moving at high speeds relative to a stationary observer. The effect is described by the Lorentz factor γ = 1/√(1 - v²/c²), where v is velocity and c is the speed of light. This calculator shows how much time slows down at any speed.
According to special relativity, a clock moving at velocity v relative to a stationary observer ticks more slowly. If the moving clock measures a time interval t₀ (proper time), the stationary observer measures t’ = γt₀, where γ = 1/√(1 - v²/c²). At everyday speeds, γ is indistinguishably close to 1. But at 90% of light speed, γ ≈ 2.29, meaning one second on the moving clock corresponds to 2.29 seconds for the stationary observer.
Time dilation is not a theoretical curiosity — it has been confirmed experimentally many times. Muons created in the upper atmosphere by cosmic rays live long enough to reach Earth’s surface only because time dilation extends their short 2.2 µs half-life. GPS satellites must correct for both special relativistic time dilation (clocks run slower due to orbital speed) and general relativistic effects (clocks run faster due to weaker gravity at altitude).
At 99% of c, γ ≈ 7.09: one year on the spacecraft equals 7 years on Earth. At 99.99% of c, γ ≈ 70.7. As v approaches c, γ approaches infinity, meaning time essentially stops for a photon from its own perspective. No massive object can reach c because the energy required also approaches infinity.