Here's a link to a great book by Steve Mcconnell (aka Mr Code Complete):
http://www.amazon.com/Software-Estimation-Demystifying-Practices-Microsoft/dp/0735605351/ref=ntt_at_ep_dpt_3 - Software Estimation Demystified
The basic steps are:
- break down the pieces to understandable/workable chunks (look into workbreakdown structures)
- if there's an item that you need more info on, note it and make sure you inform your manager ASAP
- the piece's that you have should include items that are like others you've done before - which should make it easy to provide an est. on those, items you have some 'rough' idea about how long it SHOULD take (add a % over your gut reaction time based on your comfort level - say somewhere between 10% and 30%) and those items you just have to take a wild guess at (add a % range to those, which could be anywhere from 30% to 500%)
- put you list of deliverables together in a spreadsheet, name each item, comfort level of completing (high to low), your time est. - which could be a range (min. 1 day to max 5 days) and any notes that could include questions and assumptions.
- present it to your manager and discuss
A doc to talk to that includes the items needed to be completed, questions, assumptions and a range of possible delivery dates speaks a lot for your level of programming maturity - compared to someone who throws out a # of days/weeks (or just a snide remark) and never comes close. If your manager doesn't appreciate that - find a new manager.
