I'm looking at purchasing a home and am trying to calculate affordability. I've created a Google spreadsheet which calculates my monthly mortgage commitments based on different input values (essentially different mortgage providers) and spits out a number but I want to take this one step further to determine if / how much by I need to increase my income.

I'm of the understanding that mortgage providers want to see proof of income that shows your monthly take home is at least double the monthly commitment. So I would like to calculate this from my calculated monthly mortgage estimates. However, I would like to know the required gross annual salary, not the net annual salary.


If I know the monthly take home figure, how can I calculate the gross salary taking into account the UK tax system (Just the normal PAYE, no special tax circumstances)?

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    Do you want a resource for calculating the "required gross salary" (like a website that will tell you that given a take-home of £1500 per month your gross salary would be £21,498) or do you need a formula etc to be able to calculate it yourself from first principles? – seventyeightist Feb 9 at 17:52
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    Thanks for asking @seventyeightist ! I'm looking for a formula so that I can calculate it myself. I'd like to be able to change the constants in the spreadsheet (interest rate, LTV, deposit...) and see how that changes my projections. – J. Doe Feb 9 at 18:13
  • Heavily inspired by this repo[1] I'm close to the answer using python[2]. However, comparing to this resource[3], my results seem to underestimate the required salary. Can anyone see where I went wrong? For Example: net: 24000 gross: 30322.23 stafftax: 30466.00 net: 36000 gross: 47969.29 stafftax: 48645.00 net: 48000 gross: 64852.96 stafftax: 69334.00 [1]: github.com/GaryJones/… [2]: pastebin.com/rAmEZXCy [3]: stafftax.co.uk/employers/salary-calculators/… – J. Doe Feb 9 at 20:39

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