[ser0]

The rule of thumb that I was taught for software delivery is to double it for every layer of management you have to deal with.

So if it's just you to a customer, 1 week becomes 2.

If it's you, reporting to your manager, to a customer 1 week becomes 4.

Although I generally don't apply multipliers this liberally, I do keep in mind how many stakeholders there are that can add uncertainty and friction to a project.

[chris11]

I've noticed that increasing the number of something usually indicates increases complexity. Working with another team takes more time than just keeping the work in one team. Working with two takes longer. Same with things like the number of repos, languages, or services.

[kitd]

That may be an expression of Brooks Law; increasing the number of people involved increases the average error count.