Modified Dietz
The single period rate of return formula that is widely used throughout the financial industry to combine into TWRs. It allows the placement of sub period boundaries at dates when valuation data will be available e.g., quarterly. Within these sub-periods, if a cash flow occurs, an implicit constant rate of return before and after is effectively assumed by time-weighting the cash flows in the denominator by the fraction of the sub-period duration that the cash flows affect the portfolio.