I should say to calculate this properly you need to include individual circumstances (and tax credits), but the table and graph here show roughly what daily rates are worth to you as an equivalent salary. In other words, if, for example you are working on a contract that pays €300/day, if you wanted to keep your (after tax) income the same and take a salaried role, you would need an offer of €73,929. 
Of course there are other factors to consider, but I hope this is useful.