The rate of return on your dashboard is a Money-Weighted Rate of Return, calculated net of your fees and annualized. A Money-Weighted Return is the best reflection of your overall performance, as it takes into account the money deposited to and withdrawn from your portfolio. This makes it a more personalized rate of return than other methods.
Other common methods for calculating investment returns are the Time-Weighted Rate of Return and Simple Rate of Return. The Money-Weighted Return is impacted by cash flows in and out of your account and can vary from a Time-Weighted or Simple Rate of Return which does not account for cash flows.
For people that like math, the formula is:
CF = Cash Flows
R = Return
W = (CD − D)/CD
CD = calendar days in period
D = days since beginning of period
MV = Market Value