Fixed Time, Variable Scope (Appetite-Based Planning)
Set the max time you'll spend first, then design a solution that fits it — instead of estimating a concept.
- Difficulty
- Moderate
- Time to result
- ~weeks to results
- Steps
- 3
- Confidence
- 95%
Rather than take a big concept and ask engineers to estimate it, you decide up front the maximum amount of time the business is willing to spend (the 'appetite'), then work backward to shape a version of the idea that can be truly finished in that window. Time is fixed; scope flexes to fit. Six weeks is the practical ceiling because it is the furthest most teams can see clearly enough to plan backward from.
Origin
Developed by Ryan Singer at 37signals/Basecamp and published in his 2019 book 'Shape Up.' It grew directly out of the constraint that co-founder DHH programmed only ~10 hours a week on Basecamp V1, forcing the team to use engineering time with maximum efficiency.
Core principles
- 01Never start something unless you can see the end from the beginning
- 02Set the appetite (a time budget) before the solution, the way you set a budget before shopping for a car
- 03Six weeks is a maximum, not a target — it forces the hard question of what slice you can actually land
- 04Vary the scope to fit the time; do not extend the time to fit the scope
- 05The value of the time-box is that it 'pushes back' and forces intentional tradeoffs
How to run it
- 1
Name the appetite, not the estimate
Decide the maximum time you are willing to invest before you must have something finished and shippable. Frame it as 'we'll spend up to X weeks on a whack at this,' not 'how long will this take?'
Pro tip Treat the appetite like a purchase budget — it becomes the tool you use to choose between alternatives and make hard tradeoffs.
- 2
Cap the window at six weeks
Use six weeks as the upper limit for a substantial feature. Smaller growth work can be two or four weeks; you can bundle a few small things to fill a cycle. The point is a ceiling you can see across.
Pro tip If a job feels like six months, it is unplannable — there are too many unknowns and ticking time bombs to get your arms around.
Watch out Below ~two weeks there are very few feature-level changes valuable enough to sell; you end up sprinting bite-by-bite and never seeing the end.
- 3
Work backward to a landable slice
Given the fixed time, ask what version of this could be genuinely done — not merely started — inside the window. The output is a slice you could literally walk away from and still have delivered something meaningful.
Watch out This only works if the solution has been shaped; you cannot just hand a giant project to a team and tell them to 'vary your scope' — that is, as Bob Moesta puts it, trying to put ten pounds of crap in a five-pound bag.
In the wild
On Basecamp V1 (2003), David Heinemeier Hansson was the only technical person and programmed just 10 hours a week. The team could not afford to build the wrong thing, throw it away, and start over, so they forced themselves to sharpen every idea until they were confident before David built it.
→ The habit of working backward from scarce, valuable engineering time became the seed of the entire Shape Up method.
Common mistakes
Estimating the concept instead of setting an appetite
Taking a big idea, producing figma files or a requirements doc, and then asking 'what's the estimate?' invites open-ended scope and unknowns. Reversing the order — time first, scope second — is the whole shift.
Treating six weeks as a deadline to fill rather than a ceiling
The number does its work only as a maximum. Used as a target, teams pad to fill it (Parkinson's Law); used as a ceiling, it forces the productive question of what slice can actually land.
Is it for you?
Best for
Product, design, and engineering leaders at a 30–50 person company who feel they used to be fast and are now stuck estimating and overrunning.
Not ideal for
Genuinely novel R&D where you must invent a new algorithm, database, or AI model — you cannot see the end from the beginning, so the time-box can't be honored.
From the transcript
“we're going to say what is the maximum amount of time we're willing to go before we actually finish something”
“six weeks is kind of the maximum that we could see into the future where we could actually say like how do we work backward”
“use your fixed time vary your scope”
“you can't put 10 pounds of crap in a five pound bag”
From the episode
A better way to plan, build, and ship products
Ryan Singer (creator of “Shape Up,” early employee at 37sign