Estimates can be fairly accurate if they&#x27;re made for software that&#x27;s a composition of previously iterated work.<p>If someone asks for a login system with X,Y,Z and you&#x27;ve done that 1000 times, you can be fairly accurate in stating what it will take to do it 1001 times.<p>The issue is when a piece of software is custom, and there&#x27;s no domain expertise available for the custom bit then you cannot accurate estimate how long it will take because the developers will be learning while doing.