I guess what I'm trying to achieve is a single annualised figure of how well my equities (purchased on various dates over the past few years) have performed to date. There's some winners in there and there are some losers in there. I want to use this as a measure of my ability to choose equities (fair enough it could have been luck as well!). I have had them for a good few years now so I reckon I have a long enough time period to judge. I want to use this measure then as input into some decisions; buy more directly held equities, buy ETFs or invest more in P2P lending.
Ok, that seems like a reasonable aspiration. However, you are thereby choosing a single number to characterise your entire investment history. What if you got better over time, as presumably you would hope? Also, what number are you going to compare against for an ETF or other investment in order to make your decision?
I've just come across a function in Excel called XIRR (Internal Rate of Return). So you can specify a list of dates when your portfolio was added to and and the amount that were added at that time. You can then specify a closing date and value and it will calculate an annualised rate for you.
I've attached a screenshot of the values in Excel and the formula is =XIRR(B1:B3,A1:A3).
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The value that is has come up with is 11.99%. The value that has been calculated by PMU above using the TWR method and then annualising it is 10.76% so there is a difference. What does everyone think of this formula in Excel? Using this would be much easier than going back in time trying to figure out historical value of a portfolio.
I think PMU above correctly characterised that Excel XIRR function. Just to make sure I understood what it was doing, I reproduced its results as follows (I'm reasonably savvy at maths but don't know a whole lot about investing or accounting terms):
Taking your annualised rate computed by Excel (11.99%) I computed a compounding daily rate (which is needed instead of a simple rate because it has to be used across periods of arbitrary length). I reckoned the compounding rate as:
... where
a is the annualised percentage rate. The balance at the start of each period is the new amount added (or withdrawn) plus the previous period start balance plus "interest" compounded over the length of the previous period. So as PMU said (much more concisely than I have), this is like calculating the interest rate on a bank account, taking into account deposits and withdrawals, which gets you from your opening balance to your final balance. It doesn't take into account the performance of any particular stock, or the performance during any particular period. Clearly it
couldn't, since you are choosing to characterise the entire portfolio over the entire period by a single number.
I have all of the starting values of my equities but the values of them each time I bought another equity is not something I have. I could go get all of these historical values but it would take time and some are in other currencies so I'd have to get the historical currency values as well to figure out the Euro equivalent at the time.
Intuitively, this is the missing information you would need in order to calculate a rate of return
within each period. From my (brand new
) understanding of
time-weighted return referred to by PMU, that's exactly what a TWR is. It would let you compare your performance against, say, ETFs (
like these ones) based on real historical periods. But in order to calculate rolling values like "last three months" or YTD, you'd really need daily valuations of your portfolio.