Question: I have two columns of year in excel sheet as year.months format (column first as 1.11 means 1 year 11 months) column second as 0.7 means 7 months). I need difference between two columns as year.months format. i.e., 1.11-0.7=1.4 means 1 year 4 months.

Answer: 
This approach will perform the math by converting everything to the same base units as month. You can perform the steps over multiple column which will make it easier to read, maintain and troubleshoot. When everything is working you can combine it into a single formula which will be a monstrosity that is hard to read and potentially maintain by others in the future.

For the sake of this solution, assume your 1.11 date is in A1 and you 0.7 date is in B1.

Step 1) Convert A1 and B1 to months

In C1 place the following formula and copy it to D1

```
=LEFT(A1,FIND(".",A1)-1)*12+RIGHT(A1,LEN(A1)-FIND(".",A1))

```

Step 2) Find the difference in months

In E1 Place the following formula

```
=C1-D1

```

Step 3) Convert difference in months back in to year.month format

In F1 place the following formula

```
=INT(E1/12)&"."&(E1-INT(E1/12)*12)

```

Now if you got and substitute formulas into one another so its all in a single cell, your formula will wind up looking the following.

```
=INT(((LEFT(A1,FIND(".",A1)-1)*12+RIGHT(A1,LEN(A1)-FIND(".",A1)))-(LEFT(B1,FIND(".",B1)-1)*12+RIGHT(B1,LEN(B1)-FIND(".",B1))))/12)&"."&(((LEFT(A1,FIND(".",A1)-1)*12+RIGHT(A1,LEN(A1)-FIND(".",A1)))-(LEFT(B1,FIND(".",B1)-1)*12+RIGHT(B1,LEN(B1)-FIND(".",B1))))-INT(((LEFT(A1,FIND(".",A1)-1)*12+RIGHT(A1,LEN(A1)-FIND(".",A1)))-(LEFT(B1,FIND(".",B1)-1)*12+RIGHT(B1,LEN(B1)-FIND(".",B1))))/12)*12)

```

I would not want to be someone new coming in and looking at that and trying to figure out what its doing let alone editing it 3 months down the road when a change is required.

[![POC](https://i.stack.imgur.com/N59qS.png)](https://i.stack.imgur.com/N59qS.png)

A few caveats, Make sure the date in A is bigger than the date in B. It gives bad results for negative values. Also ensure there is always a "." in the date or errors will ensue. If there is a 12 month difference it will currently display 1.0 as the difference instead of 0.12. If the later is required, a special case would need to be developed for when there is differences resulting in multiples of 12 differences.
Let's say `A1=1.11` and `B1=0.7` then formula would be:

`=LEFT(A1;FIND(".";A1;1)-1)-LEFT(B1;FIND(".";B1;1)-1)&"."&(MID(A1;FIND(".";A1;1)+1;2)-MID(B1;FIND(".";B1;1)+1;2))`

[![enter image description here](https://i.stack.imgur.com/UC54d.jpg)](https://i.stack.imgur.com/UC54d.jpg)