Outruntime.
Pick a destination on the map. Set your speed. See how much less you'd age on the round trip — the faster you go, the more Earth's clock runs ahead of yours .
Solar system
interstellar void
Nearby stars
Milky Way
Intergalactic
Proxima Centauri
Closest known star to the Sun
Distance
4.24 light-years
Constant velocity traditional
Constant acceleration realistic
Presets
0.1 c
0.5 c
0.9 c
0.99 c
0.999 c
0.9999 c
Presets
0.1 g
0.5 g
1 g
2 g
3 g
5 g
On Earth
—
while you're gone
For you
—
on the spacecraft
You return — years younger than your Earth-bound twin.
Doppler shift · outbound
—
Sun's yellow light (550 nm) reaches you as:
—
Inbound trip is the inverse — blueshifted by the same factor.
Length contraction · your frame
—
In your frame, the destination has moved closer — not your ship that's gone further.
Photon rocket · mass ratio
—
Launch mass per kg of payload returning home (4-phase trip)
—
Theoretical maximum efficiency — matter / antimatter, fusion, and fission all require vastly more.
Reference duration
year(s) far from the well
Far from the well
—
asymptotic / reference observer
At location
—
local proper time
Select a scenario above to see gravitational time dilation.
The math
γ = 1 / √(1 − v²/c²)
t_earth = 2d / v · τ = t / γ
Doppler: λ_obs / λ_emit = √((1+β)/(1−β))
L_obs = L_rest / γ
M₀ / M₁ = ((1+β)/(1−β))c/2vₑ
τ_local = t_far · √(1 − rₛ/r) · rₛ = 2GM/c²
Trips assume the constant-acceleration phase ignores fuel mass loss (treats payload as instantaneously massless). Real trips amplify mass ratios further.
Caveats
No spacecraft has ever exceeded 0.0001% of c. Real round trips would need fuel, life support, and the ability to survive turnaround.
At v→c the energy required diverges. This is a physics calculator, not a travel itinerary.
Constants
c = 2.998 × 10⁸ m/s
1 light-year ≈ 9.461 × 10¹⁵ m
1 light-day ≈ 173 AU
Distances are typical/average; planetary distances vary with orbital position.