Short answer
There is no single exact gross salary for everyone
Two people can aim for the same £3,000 monthly take-home pay but need different gross salaries. Pension contributions, student loan plan, region and tax code can all move the answer.
The cleanest way to estimate it is to start with a reverse salary calculator, then add the deductions that apply to your real payslip situation.
What changes the number
The assumptions that matter most
The largest drivers are usually Income Tax, National Insurance, pension contributions and student loan repayments. Scotland can also change the Income Tax result because it uses different tax bands for Scottish taxpayers.
Decision use
Use the target as a planning number
A £3,000 monthly target is useful for rent, bills, savings and lifestyle planning. Treat it as a planning estimate, then compare it with a real payslip once the salary is confirmed.