I just started to obtain historical data from Interactive Broker via calls to it's API then I will feed the daily bar prices ( open, low and close) to my algorithms to generate signals.Further examination found that IB seems to adjust the closing equity price 1 day before the ex-dividend dates, and this adjustment happens only for one day closing price. If t= ex dividend datePt-1 = P original close - abs(dividend)Although this approach is slightly different from Yahoo Finance (% adjustment to prevent adjusted price from going negative) but I guess I can apply the adjustments to all pre ex-dividend date data myself for IB price series. So this is not a worry to me. However, I found quite a few cases that IB missed adjustment to the most recent dividend, say t0 is today, the March Pt-1 is adjusted but not for the Sep Pt-1, even for some very liquid large cap blue chip stocks.I have called IB support trying to get some answers but they are very slow and for those are still working during Xmas they seem to have no answer.So my question is:(1) is this consistent with your understanding of IB's treatment on historical dividends?(2) How reliable, based on your experience, is IB's historical data? especially on the adjustment part.(3) if there is any other reliable sources that I can get dividend/split adjusted open,cl,high,low end of day prices for Australian equities? I know you find good data for US equities but I am struggling to find the Aussie ones.Thanks in advance!

I have had the same problem and never found a good answer. MSN, FT.com, MorningStar, Yahoo, IB etc all keep dividend and split history but it is often incomplete or applied at the wrong time. It makes backtesting a nightmare. I'm guessing you could improve the quality by taking several sources and aggregating them, or paying more to a private vendor who is claiming to offer better history.

I just checked one year's of bars for SPY (S&P 500 ETF) that I imported from IB and compared them against Yahoo's data.It does not appear that IB makes any adjustments for the dividends that were paid.