I think the reason youпїЅre not getting an answer is because it looks like what you actually want is someone to tell you the exact formula to enter and thatпїЅs impossible without knowing what tax you pay!
YouпїЅre going to need to do some maths yourself. Look at a recent payslip and work out from the deductions column what percentage of your gross salary is being deducted as NI and tax and any other deduction you want to calculate. Forgive me if you already know this, but the annual personal allowance is averaged out over a tax year, so you pay a bit every time even though you can earn пїЅ5035 before tax kicks in.
To use this info in an excel spreadsheet you must have a cell that contains your gross salary and then another
cell that contains the formula to get the result. ItпїЅs probably easiest if you have a cell for every deduction and then add them up at the end to get the final net amount.
For example, A1 would be пїЅ8000 per year. B1 would be =SUM(A1/12) to get your monthly gross. C1 would be =SUM(B1*20%) to find out what 20% of your monthly salary would be. D1 would be =SUM(B1*7%) to find out what 7% of your monthly salary would be. E1 would be =SUM(C1+D1) to show your total deductions. F1 would be =SUM(B1-E1) to show your net total.
Once you do the maths youпїЅll realise itпїЅs a bit more complicated than this, but this should get you started.
Hope this is what you meant. Otherwise youпїЅre going to have to ask your question again differently!