Use the XIRR function, which in Excel looks is represented as XIRR (values, date, Guess). Lastly, choose values for a series of cash flows corresponding to the payment schedule in the date column. Ensure you mention the investment dates in the date column, along with when you obtained the...
due to non-business days, the spacing will be greater/less than 365 or 30 days. The spacing does not matter for XIRR. If the spacing is exact, things become simpler and this is often known as an IRR calculation.