i ran analysis on our codebase, most of the files had 40% rewrites, with some outliers being 90% rewritten. the file sizes followed linear distribution, usually from 100 to 2000 lines of code. when the 90% rewrite hit a larger files, it accounted for almost 50% of total effort put into development. what i got from this, for a single component i take the ideal estimate then multiple it x2, and do the same x2 project wide. there's additional friction when integrating outside components, but i'm rarely blamed for it, so i don't care that much to put it in estimates.
now the hard part is selling the idea to the management, like "here are our ideal estimates, lets multiply it by 4". when doing freelance work i usually bill for the ideal estimated time multiplied by 2, the rest being my risk, on the other hand any changes in the requirements, or miscommunication is a risk of the client.
now the hard part is selling the idea to the management, like "here are our ideal estimates, lets multiply it by 4". when doing freelance work i usually bill for the ideal estimated time multiplied by 2, the rest being my risk, on the other hand any changes in the requirements, or miscommunication is a risk of the client.