No, that isn't possible, since the amount on each row needs to be multiplied by the percentage for that row to get the value for that row, which then has to be aggregated with the values for the other rows calculated in like fashion, then divided by the grand total to get the weighting. Word tables & formulae don't have the functionality of Excel, which is what you really should be using if the row count varies. If you were to use an Excel workbook, you could either embed it or an OLE link to it in the document. In the latter case, if you use a named range that varies according to the amount of data, the embedded object in Word will resize to accommodate the changes.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]