Excel - Sum values if their row meets more than one criteria

I have a spreadsheet of my bank account transaction history in this format:

  | A          | B        | C        | D
1 | Date       | Amount   | Balance  | Category
2 | 2013-03-10 | $ -10.59 | $3700.76 | Food shopping
3 | 2013-03-11 | $ - 5.10 | $3695.66 | Car parking
4 | 2013-03-11 | $ 100.00 | $4695.66 | Salary

In my spreadsheet the Balance column is hidden because I recalculate it myself.

I want to have a summary for each month with data looking like this:

  | A       | B        | C           | D
1 | Month   | Income   | Expenditure | Net
2 | 2013-03 | $ 100.00 |     $ 15.69 | $ 84.31
3 | 2013-04 | $  00.00 |     $ 00.00 | $ 00.00

These are the formulas I have right now, so I can compute Net fine, but I don't know how to compute Income or Expenditure on a monthly basis because SUMIF only lets me do criteria on a single column (in this case, the Date column, but I want to only sum rows >0.0 for Income and <0.0 for Expenditure):

Net = =SUMIF( MonthAndYear( Txn!$A:$A ) , $A$2, Txn!$B:$B )

Answer

You can use SUMIFS to sum with multiple conditions. For example:

=SUMIFS(B1:B6,A1:A6,"2013-03",B1:B6,">0")

This assumes your month column is a string and not a date. Because SUMIF only allows direct comparisons and cannot run a function on the month column. So it could not convert a date to a number for example.