Why your estimates are off, and what to do about it
If you're regularly off by 20% or more, the issue isn't bad luck. It's a missing input.
Track estimate vs actual every job
A simple spreadsheet column for estimated hours and actual hours, every job, for 90 days, will reveal exactly where you're systematically wrong. Almost every owner is off in a predictable pattern.
Add a contingency line you actually use
10 to 15% built into every estimate covers most surprises. Don't shave it off to win the bid. The shaved-off jobs are the ones that hurt.
Walk the job before you quote it
Phone estimates and Google Earth measurements look fast and feel modern. They're also the source of most of the misses. The drive is part of the quote.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.