Average Formula that counts blank cells

Hi folks,

Is there a formula for working out averages that INCLUDES empty cells in the calculation?

Say you pay for something quarterly and it looks like this:

Jan - £120
Feb -
Mar -
Apr - £120
May -
Jun -
July - £120
Aug -
Sep -
Oct - £120
Nov -
Dec -
Total - £480
Average - £120

Just using the "Average=" formula would return £120, and I'd like it to say £40.

I know this is a bit tedious especially as there's 2 relatively easy and quick fixes in that I could:
1) Manually type in the 0s in the empty cells
2) Set the Average row formula to just be "Total / 12" instead of an average.

I was just wondering if there was a "proper" way to do it?

That does the job beautifully. Thanks.