Spoke with a potential client about delivering a computer vision app. I estimated this would take one month, erring on the side of a conservative estimate to account for any complexities that might unexpectedly bubble up. However, I didn't realize just how conservative it was compared to another iOS engineer's estimate of 60-80 hours when he told me. He also said that a number of his contacts agreed that 60-80 hours sounds right.

How might I avoid such a discrepancy of 2-3x in the future, and potentially navigate situations like this?