If you look at the reputation tab of my profile, the graph ends at a score of 12k5, my actual score is 14k8.
I have been deleting some answers lately, some with votes. Could it be that the graph is showing what a ReCalc would do?
Adding up all the green numbers and subtracting all the red numbers gives 12211. So that's the reputation you'd have from all current questions and answers.
Edit: I hadn't realized that this list also includes reputation used and granted for bounties - given that it does, you can probably trust this number. Keep in mind, rep from deleted answers, including answers to deleted or migrated questions, doesn't count.
At one time, I had a Greasemonkey script written to calculate your actual reputation from the graph... But this was never perfectly accurate, and the addition of the /reputation page (for instance, your Stack Overflow reputation audit) makes this unnecessary.