Self Employed Tax Return - tax on profit (and pension) query

Mick70

morning all,  if wifes tax return (self employed) shows 
Turnover  12k
Allowable expenses 5k
Net profit    7k

I take it for any tax you need to pay it is based on the Net Profit ?  and that NP can be up to £12.5k before pay any tax ?
also, does anybody know for pension purposes , can she pay into her pension pot only a limit of the 7k  or is it  the 12k ?  (in order to get the govt top up?)

many thanks
micl

Dazed_and_C0nfused

If she hasn't applied for Marriage Allowance and has no other taxable income then net profit needs to be £12,501 before may tax would be payable (for 2019:20).

Class 2 and Class 4 National Insurance have lower limits so they may be payable even if no tax is payable. 

She can only contribute £5.6k to a relief at source pension.  Which will get the 25% top up to make a gross contribution of £7k.