Tool
Do you build it or buy it?
Two cumulative cost curves with your team's numbers, and three questions the curve cannot answer. The values shown are an example so you can see how it works, not a market average.
If you buy it
If you build it
Over 3 years, building it comes out USD 45,500 cheaper. Buy: USD 439,000. Build: USD 393,500.
When it pays for itself: From month 23. Until then, what you have spent building is still above what you would have spent buying.
Engineering that goes in: building and keeping it consumes 41 engineer-months inside the horizon. Buying it, 1. That time is not turned into dollars here, because that number would be ours: put your own price on whatever that team stopped building.
What comes with the platform and is not software
Replacing a platform means replacing the operation that came with it. Mark what already has somebody on your team, by name, who owns it.
5 of 5 with no owner. Each one is an on-call shift or a task with a name on it. The maintenance you entered (USD 8,500 a month) has to be enough to pay for them, or the saving on the curve does not exist.
Three questions the curve cannot answer
Cost answers one of the two questions. The other is whether this is yours or whether it is infrastructure. The first two yeses together are what make it yours; the third is not a reason to build, it is a condition for being able to.
It is a saving on paper. The curve favors building, but nothing you answered says it is yours. That saving exists only if maintenance stays where you put it, and it is paid in on-call shifts and in engineers who are not improving the product.
The model, in plain sight
Buying is the integration months times the cost of an engineer, plus the license for every month. Building is the engineers times their cost times the months of building, plus the license for those same months if you pay it today, plus the maintenance times its cost and what you pay outside, for every month from launch. Every value is yours and the opening ones are an example, not an average. We do not turn what that team would have built instead into dollars: that number would have to be yours.
How to read it
- The two curves do not start from the same point. The build curve rises from the first month because you keep paying for the platform until the replacement is in production. Switch that option off to see how much it weighs.
- Look at the slope of the build curve after the dotted line. If it is close to the buy curve, the saving never arrives: maintenance eats it.
- The sum alone does not decide. Move it until it favors building and answer the three questions: if the verdict turns into a saving on paper, the sum was lying by omission.
This is the interactive half of an article about what you actually replace when you replace a platform. Read the article