Catch-Up Calculator

You missed the roll-out. How hard, how far, and how long before you're back on the wheel?

The group

Their speed mph

You're late by min

Route length (optional — do you have enough road?) mi

You

Your speed mph

What speed do I actually need?

Required cruise speed, assuming they hold the pace above and never soft-pedal:

To be on the wheel…	You need	Over

What that costs in watts

A steady-state estimate: rolling resistance, aerodynamic drag, and gravity if you give it a gradient. No wind, no accelerations. Every number below is editable — the defaults are a mid-pack road rider on a decent road bike.

Rider + bike + everything

Position (frontal drag, CdA) m²

Surface & tyres (rolling, Crr)

Gradient %

Air density (1.225 at sea level and 15°C; ~1.10 high and hot) kg/m³

Draft benefit in the group %

	Speed	Watts	W/kg

Drag rises with the cube of speed, so these numbers are only as good as the CdA you feed them, and CdA is the hardest thing on this page to know about yourself. If you have power-meter data, fit your own: hold a steady speed on a flat road in still air and solve backwards.

Why the real chase is usually shorter than this

Stoplights. Their moving average is not their clock average. A group that averages 18 mph on Strava spends real minutes stopped, and you close the gap for free at every red light you don't hit.
Regroups. Any ride with a no-drop clause waits at the top of a climb or at the turn. Time the chase to a known regroup point and the arithmetic below is a worst case.
Draft. The numbers here put you alone in the wind and them in a paceline. That is the whole cruelty of a late start: they are going faster than you at lower cost.
The first mile. Nobody rolls out of the parking lot at cruise speed. Your first two minutes are slower than the input; theirs were too.

The math

Head start — how far up the road they are the moment you clip in:

gap = their speed × (minutes late / 60)

You only close that gap at the difference in speeds, so:

time to catch = gap / (your speed − their speed)
distance to catch = your speed × time to catch

Which is why 1 mph faster is close to useless and 4 mph faster is a different ride: the denominator, not the numerator, does all the work.