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A calculator that takes into account portfolio rebalancing?
My answer is Microsoft Excel.  Google "VBA for dummies" (seriously) and find out if your brokerage offers an 'API'.  With a brief understanding of coding you can get a spreadsheet that is live connected to your brokers data stream.  Say you have a spreadsheet with the 1990 value of each in the first two columns (cells a1 and b1).  Maybe this formula could be the third column, it'll tell you how much to buy or sell to rebalance them.   then to iterate the rebalance, set both a2 and b2 to =C1 and drag the formula through row 25, one row for each year.  It'll probably be a little more work than that, but you get the idea.