SolarEclipses.com

Delta T Calculator

Enter a date and time, or choose a solar eclipse. Select UTC, UT1, or TT, then Calculate. (See the ΔT data on a graph)

Selecting an eclipse loads its greatest-eclipse TT epoch.
Uses this computer's system clock and enters the instant as UTC.
Time scale:
ΔT = — s
DUT1 = — s
Source will appear here

About this calculator

This calculator returns ΔT = TT − UT1 and DUT1 = UT1 − UTC for dates from 1900 through 2200. Enter a date and time as UTC, UT1, or TT, or choose a solar eclipse to load its greatest-eclipse TT epoch automatically.

Every result is identified in text by its evidentiary category and exact source; color provides a redundant visual cue rather than carrying the meaning by itself. Historical/reconstructed values, observed/calculated IERS values, predictions, and long-range modeled values are explicitly distinguished.

Modern values are derived from Earth-rotation data and interpolated to the requested instant. The method and data page documents the equations, source files, interpolation procedure, update process, and enough information to reproduce the calculation independently.

Method & data documentation →