Comparing and show the difference between data in two excel tables

I've tried alot of things and i'm going blind on this comparison-project. I keep feeling it's so simple, but i just can't get it to work and therefore i hope you clever people can help me out.

I have two separate tables of data over employee salary - one with projected salary and one with actual salary. They look like this:

Projected salary
Employee-ID   Name      Position     January    February 
001           Jens      Service      1000       1000
002           Peter     Boss         1000       1000
003           Brian     Service      1000       1000

Actual salary
Employee-ID   Name      January    February 
001           Jens      1500       1000
002           Peter     500        1000
004           Janne     1500       1000

I need to combine the two list and see the difference. In this case i would like my table to look like this:

Difference in salary
Employee-ID   Name      January    February 
001           Jens      +500       0
002           Peter     -500       0
003           Brian     -1000      -1000
004           Janne     +1500      +1000

As i need to update this data every month, i would like a function/script/table, which updates by itself, when the Projected and Actual salary tables are updated.

Is it possible to find a solution and/or do you have any hints? I'm not necessarily looking for a full solution, but i will be totally fine with a guide or tutorial sending me in the right direction (i have googled a bit, but i might just be too dumb to find it.)

As this is my first time using StackOverflow, i hope this post is up to the standards of which information is needed and in the range of fair requests. Else, be welcome to point me in the direction of making better requests, as i would love to improve.

Best regards