It depends a LOT on what you're estimating. Estimating a CRUD line of business app is very much doable. On the other hand, estimating an innovative product usi

It depends a LOT on what you're estimating. Estimating a CRUD line of business app is very much doable. On the other hand, estimating an innovative product using unproven tech or novel methods requires a proof of concept before even knowing feasibility. I worked with major consultancies, and the most serious gave you order-of-magnitude estimates, with iterating improvements on the estimation itself until you reached a +/- 15% estimation that was the best they could do. Very similar to: https://www.construx.com/software-thought-leadership/books/the-cone-of-uncertainty/ https://www.construx.com/software-thought-leadership/books/t... In those cases, it was a very reasonable estimate because they'd done very similar things before. One of those consultancies used an tool and they had measured their teams' velocity and were very confident on their estimates. For one of my own projects, we had to estimate a rewrite of an existing app (with slight improvements), which is as easy as it can get in regards to estimation. We used several approaches, the one that ended up being closest to reality was Steve McConnell's tool Construx Estimate (no longer available but you can find a mirror here: https://web.archive.org/web/20170920093850/https://www.construx.com/Thought_Leadership/Books/Survival_Guide/Resources_By_Chapter/Construx_Estimate/ https://web.archive.org/web/20170920093850/https://www.const... )