Feedback on salary calculator.

[j.crater]

Hello, it looks pretty good to me.

National_Insurance = 12 # 12% after £183
Tax_Limit = 37000
Tax_Allowance = 12500

Usually constants are found in the beginning of code (and after imports, if there would be any, but not in your case).

Yearly_Tax = round(Weekly_Tax * 52,2)
 
Weekly_Take_Home = round(Weekly_Income - Weekly_NI - Weekly_Tax,2)
 
Yearly_Take_Home = round(Weekly_Take_Home * 52,2)
 
 
Monthly_Take_Home = round(Yearly_Take_Home / 12,2)

I would not leave any blank lines between these statements, but that is up to your preference.

Monthly_Take_Home = round(Yearly_Take_Home / 12,2)
Monthly_Take_Home = round(Yearly_Take_Home / 12, 2) # a whitespace after comma

Also in cases like this, a whitespace after comma is recommended.

Otherwise, pretty good! You can try to open the file in a code editor and select code formatting option to do an automatic check for you. Or run a PEP8 check on the code.
It seems like online checkers exist too, I wasn't aware of that before: http://pep8online.com/