The general strategy of adding estimates up from zero means you will always underestimate, and that deficit will grow with the size of the thing you are estimating.

2025-07-09T12:53:21Z

Estimate the effort it will take to deliver a unit of work product before committing to a budget and/or schedule.

https://www.infoq.com/articles/estimation-game-techniques-for-informed-guessing/

Just pad your estimates. Double, even triple them.