Freelancer calculatorEdit on GitHub
At the same time I work as employee, sometimes I get offers for freelance projects. It's difficult to find a balanced rate between both schemes, so using Google Spreadsheet I've done a calculator to adjust them. The calculator is focused for Spain taxes (one of the reasons texts are in spanish), but should be easy to addapt to other normatives.
The spreadsheet has three tabs, one with the calculator from employee to freelance, another from freelance to employee, and the third one to store tax due percentages and costs. They are very easy to use, just only needs to set the anual gross salary (Spain's standard way to negotiate employee salaries) or the daily rate (the most common way I've found for international freelance projects) and you get the equivalent salary ranges in hourly, daily, monthly and anual rates for same final net salary in both schemes, same gross (somewhat useless, but interesting), or same costs to the company (specially interesting to be used as your target freelance rate: you ask for less, they earn money; you ask for more, you'll be cheaper to them contracted as employee ;-) )
Please note that I've found it gave me some differences regarding to what I used to ask for freelance projects... When doing previously the calcs, I used a quick relationship between employee NET salary and freelance daily rate of 150:1 for company equal costs (and also, a couple of companies that gave me the oportunity of working in any of both schemes already referenced that relationship by themselves), but the calculator gave me a relationship of 200:1, so I'm not sure salaries are low in Spain (they are, but not so much to have such a difference), I was asking for too much money (companies has already paid for it, so probably not), or there are more hidden costs I need to add the calculator. Your mileage may vary... but also, improvement comments are welcome :-)
For the future, it's pending to add support to calc different rates for international projects (between European Union countries there's compensation of tax dues, but for outsiders it's needed to add full taxes in your rate... or you'll end up paying them from your pocket), and differences between life level costs, specially when relocation is needed and accomodation is not provided by the client (yes, that's more common than what's desirable, and it feels really annoying and unprofessional by their part to all the freelancers I've talked about...).