change the total while the data change in different column

[PINO]

For example...
A1 thru A12 are Month from Jan. to Dec.
B1 thru B12 will have number as the month goes by...
B13 will be my end result...

What I am trying to figure out is how to set the formula in B13 t
change when I modify the number between B1 to B12.
i.e., when I put the number in B1, the B13 will equal B1.
After that, when I put the number in B2, the B13 is now equal t
B2.
And so on.... I wanna have my B13 always equal the the lastes
number I put in.

How do I do that?
Please help...
Thank yo

 

[Dave Peterson]

=index(b1:b12,counta(b1:b12))

If you never have gaps in B1:B12.

=LOOKUP(2,1/(B1:B12<>""),B1:B12)

Will work with or without gaps.