This would've worked if you'd taken your initial estimate (1 week) - bumped it to the next unit (1 month) - then doubled it (2 months). Maybe you would've been

This would've worked if you'd taken your initial estimate (1 week) - bumped it to the next unit (1 month) - then doubled it (2 months). Maybe you would've been given 9 or 10 weeks, so you'd have the week for X, and 1 month each for Y and Z. I understand this is a contrived example, but it's strange that, when you take a real project that "overran" based on the initial estimate(s), and you apply the formula - just how often the formula is actually really close to the actual amount of time. Not always - but more often than not.