EPOCH

time-scale converter

UTC NOW —

format

How the scales relate

UTC — Coordinated Universal Time: Civil time, kept near Earth rotation by whole-second leap steps. TAI = UTC + ΔAT, ΔAT = 37 s today.
GPS — GPS Time: The atomic scale broadcast by GPS satellites. Constant GPS = TAI − 19 s, so it runs 18 s ahead of UTC now. Conventionally counted in seconds from its 1980-01-06 epoch.
TAI — International Atomic Time: The continuous atomic reference, with no leap seconds.
TT — Terrestrial Time: Timescale for geocentric ephemerides. TT = TAI + 32.184 s exactly.
TCG — Geocentric Coordinate Time: Coordinate time of the geocentric frame. TT is TCG re-scaled to tick at the geoid: TT = TCG − L_G·(t − T₀), L_G = 6.969×10⁻¹⁰ — TCG gains ≈ 22 ms/yr on TT (~1.09 s today).
TDB — Barycentric Dynamical Time: Differs from TT only by periodic terms (≤ ~1.7 ms). Seconds past J2000 in TDB is SPICE Ephemeris Time (ET). Sine model: TDB − TT ≈ 0.001658·sin g + 0.000014·sin 2g.
TCB — Barycentric Coordinate Time: Coordinate time of the barycentric frame. TDB = TCB − L_B·(t − T₀) + TDB₀, L_B = 1.5505×10⁻⁸ — TCB gains ≈ 0.49 s/yr on TDB (~24 s today).
Format: One format applies to every row at once — ISO 8601, JD, MJD = JD − 2400000.5, seconds past J2000, Julian epoch, or Unix time — each shown in that row's own scale. It governs both display and what you type in. An ISO string carries a Z only for UTC.