Relativistic Time Dilation Calculator
Compare proper time with coordinate time at constant relative speed.
Apply the Lorentz factor to elapsed time
Special relativity links proper time on a moving clock with coordinate time in an inertial frame through the Lorentz factor. This calculator accepts speed as a fraction of light, computes one divided by the square root of one minus speed fraction squared, and multiplies proper time by that factor. The time unit is preserved, so seconds, years, or another consistent unit work.
At 0.8 times light speed, the Lorentz factor is 1.66667. A proper interval of one year aboard the moving clock corresponds to 1.66667 years in the frame where that clock moves at constant speed. At low speed the factor approaches one; as speed approaches light speed, it grows without bound for an object with mass.
Keep frames and acceleration outside the shortcut
The shortcut compares inertial frames at constant relative speed and does not by itself solve acceleration, turnaround, gravity, simultaneity conventions, or complete travel scenarios. Speed fraction must remain below one. Calculations are local to your browser. Interpret proper time as the interval measured by one clock along its own path, and state which frame measures the dilated coordinate interval.
Frequently Asked Questions
What is proper time?
Proper time is the interval measured by a clock that is present at both events along its own worldline.
Why can speed not equal light speed?
The Lorentz factor denominator reaches zero, and objects with nonzero rest mass cannot reach light speed.
Does this solve the twin paradox?
No. A full twin scenario includes changing inertial frames and acceleration during turnaround.
Browse the full set of free, private, in-browser tools.