I was thinking of starting STI ETF DCA and this thread came up at the right time. Though I have not done the maths, adding X% to the calculated returns to account for dividends is a quick way to estimate overall returns and should not differ too much from actuals. Dividend reinvestment is another ball game altogether and isn't easy to model, notwithstanding the lack of data pre-ETF days.
I did up a Google sheet to work out the numbers with similar assumptions as TS using XIRR to calculate the returns and got quite close to TS numbers. Added in the holding periods from 1 to 20 years since its all formula based
I can share the Google sheet link if anyone is interested.
Total Returns = Capital Gain + Dividend Yield
What I did is just the Capital Gain portion only. If you know the average dividend yield, you can safely add the dividend yield if you choose to reinvest the dividends. You will get quite close to an actual and average Total Returns.
The reason why I did not include dividends because I don't have the EXACT dividends data as I am dealing with ST Index from a very long period of time. I can only get those recent dividends data from the STI ETF.
The formula I used is the exact same formula if you use XIRR. The same formula you use when you calculate annuity or mortgage rate. So yes, the numbers should be close if you use XIRR. The slight difference is probably due to the difference in date.
Anyway, it is good that someone has verified the numbers. If not, there will be non-believers who will doubt my numbers.