This is a calculator meant to compare UK salaries, to provide a clear NET income while comparing two different salaries, due to taxes and national insurance contributions the NET income is not clear at all.
You can also use it to find out your total net income without having to compare to another salary. Find out your hourly, daily, weekly, monthly and yearly income rates.
The calc is done with class 1 national insurance contributions in mind, which is the most common case.