Calculating length of time based on one of two dates

Hi,
Hit a brick wall with Excel 2007, I know embarrassing that we are still using it.

I am trying to monitor the length of time someone is on a treatment for based from a start date to today or an end date.

I am looking for the time in months.

I have used this to calculate the time from start to present

=(YEAR(NOW())-YEAR(J6))*12+MONTH(NOW())-MONTH(J6)

I have the following columns,

Status Date of Death Date started Date stopped Total Length on treatment Current length on Treatment


I would like either Total Length on Treatment or Current Length on Treatment not both running at the same time

I have tried various IF functions but just cannot get it to work.

Your input is greatly appreciated.
Oh and to complicate matters we cannot have any macros. Not allowed in the organisation.

Cheers.

This is revised for the column so it accounts for no start date:

=IF(A2<>"",IF(B2<>"",DATEDIF(A2,B2,"m"),DATEDIF(A2,NOW(),"m")),"")

Thank you.
That does work but I was wanting to be able to distinguish between those on treatment and those off treatment.
I could try conditional formatting but is there any way to do this with a whole sheet?
Cheers

maybe split it in 2 columns one for current and one for ended?

I tried that, but to save confusion I did not want both columns to be populated and that is where I ran into difficulties.

How else would you logically determine if it is current or not?

I thought that if the date was not entered into the date stopped column then we could use today as the date in the current length of treatment column to give us the on-going duration in months
and
if there was a stop date then there would be a duration in months in the total length of treatment column.
If that made any sense
What you gave me works and I will use it, thanks

Perhaps a highlight rule that will show red when it ends?

Maybe try something like the example :

excellent, almost there bebo.
Small challenge is when there is no data in the date started column the current length of treatment defaults to 1416 months.
I had that before and it drove me crazy because it was so untidy The length on treatment defaulting to 0 is just about ok.
Billy, I will have to wait until I get home as IT security won't let me download it

Hi Bebo,
I am getting an error message to do with "m" I cannot work it out.
Cheers.