How can I calculate the mean of all months until now?

I have a column with a value for each month, like: 1,2,3,...,12. And I have a row with 12 开发者_如何学运维cells (each corresponding to a month). And I have another cell that says the current month. My question is: How can I calculate the mean of the values until the current month?

I was doing something like « =MEAN(IF(S4>S16;D4:O4;IF(S4>S15;D4:N4; IF(S4>S14;D4:M4; ...)))) »

S4 is the current month; S5 = Jan; S16 = Dec; D4 = value of Jan; O4 = value of Dec

I'm sure there is a better way to do this.

Difficult to tell exactly what you want from your question, but the following takes the average of the values of S4 rows (months) starting from D4 (the first month):

AVERAGE(OFFSET(D4,0,0,S4,1))

If you want to copy that around, be careful with your absolute references ($) (e.g. you would want at least D$4).