To work out a roughly how many hours and days you will most likely be working as a contractor, ie invoicable hours per year.
To work out a rough contracting rate based on your existing permanent salary and a few other factors.
To give an idea how much you could earn on a specific rate per year.
With a quick rough comparison to a permanent salary.
How much does actually an extra 25 per day mean? How does that change my annual revenue/income? Will a three weeks delay negate the difference?