With experience you can account for this. What's hard to account for is some 3rd party vendor blowing you off, or slow rolling you, for weeks. Or management p

With experience you can account for this. What's hard to account for is some 3rd party vendor blowing you off, or slow rolling you, for weeks. Or management pulling you into another project. Each integration point with a 3rd party automatically adds an extra 1 week+ to my estimates, depending upon the complexity.