I posted a similar chart on another thread
a week or so ago. Unfortunately I don't have a breakdown of investment return and contribution either. For me, exponential growth was pretty constant over the first 10 years or so at 18%, and then growth slowed down to 12%/yr at the end of 20 years as the annual contributions became a smaller and smaller proportion of the total. The average dollar growth per year has climbed by a factor of about 6 over those 20 years.