To estimate in the right order of magnitude, you need:
- no introduction of new technology or framework for the wanted feature;
- to separate your estimate in pure development time and availability of developers (and customer and tester..;
- to get feedback on your earlier estimates;
- a size of feature in your safe estimation range (not 2 times as large with 2 times more people)
- a stable development team.
- no project startup overhead.
- to only estimate for work you do yourself.
