From Startup Fortune · · 2m
How To Calculate Your Startup's Bus Factor Before It Costs You
A startup's bus factor reveals who could break their codebase if they left, and how to fix it without new hires.
In brief
A startup's bus factor reveals who could break their codebase if they left, and how to fix it without new hires. A startup's bus factor measures how many people must leave before code becomes unmaintainable; reducing it prevents costly failures. Originally reported by Startup Fortune.
Quick answers
- What is bus factor?
- Bus factor measures the smallest number of people who, if they quit tomorrow, would leave your codebase unmaintainable.
- What is the key takeaway from How To Calculate Your Startup's Bus Factor Before It Costs You?
- A startup's bus factor measures how many people must leave before code becomes unmaintainable; reducing it prevents costly failures.
What is bus factor?
Bus factor measures the smallest number of people who, if they quit tomorrow, would leave your codebase unmaintainable.
Left-pad incident shows bus factor 1 consequences
In March 2016, developer Azer Koçulu unpublished an 11-line npm package called left-pad, breaking builds across the internet.
2016 study reveals most projects have bus factor 1 or 2
A 2016 academic study of 133,000 GitHub repositories found most popular projects had a bus factor of just 1 or 2.
How to calculate bus factor yourself
Run git log for each repository, count contributions weighted by lines changed and commit frequency over the last 12 months.
Bus factor 1 on critical services is existential
A bus factor of 1 on payments, auth, or deploy infrastructure costs customers or money before morning.
Why git blame alone understates risk
Commit history shows who touched code but not who understands why it's shaped the way it is.
Tribal knowledge concentration matters more
Ask engineers to list three systems they'd be nervous handing off with one week's notice and cross-reference answers.
Mandatory code review reduces risk
Mandatory code review with rotation forces exposure over time without slowing down the team.
Pairing on critical systems works faster
Pair on legacy billing jobs instead of new features to expose risk faster.
Documentation prevents knowledge loss
A single README per service answers what it does, why it exists, and who last touched it.
Prioritize critical services first
Rank services by revenue exposure before running bus factor calculations on top of that list.
Fix bus factor before it costs you
The calculation takes an afternoon; waiting for a crisis costs more than the time spent.
The short version
A startup's bus factor measures how many people must leave before code becomes unmaintainable; reducing it prevents costly failures.
