Got it - then can't you just use your starting balance regardless of the start date? And, to your point, just factor in any contributions by subtracting them out.

I was just giving the general guideline. You can be as precise or specific as you want. I used to work for the largest mutual fund company on the planet and we would do attribution analysis at a trading level that would make your eyes bleed. But, I don't think that's exactly what the OP was referring to.

9.25% but i have under $10k

starting balance sept 1 was $0

9.35%

down 6% but that was mostly because of a large BAC purchase. I have a very long horizon and they have 300 Billion in cash

I did badly last year...

I am at exactly 0% in the 2 hours since I bought stocks today. Add $20 of commissions, I am down $20.

Google Finance is very good for tracking your returns. If you import your transactions, it will let you run a chart for a specific time period.