No, you declare actual figures. I said 3 times a year because I assumed you would declare quarterly, it seems less hassle to me - the deadlines for the quarterly declarations are 30 April for your turnover during Q1 (1 Jan to 31 March), 31st July for Q2 (1 April to 30 June), 30 October for Q3 and 31 January for Q4. But you can declare monthly if you refer. Either way, in case of a contrôle you need to be seen to be invoicing promptly, collecting payment on time, and declaring everything when you should, you don't have any discretion to delay invoicing or hold receipts back from your declaration to benefit yourself. It's to your advantage in any case - if you have a crap quarter then your cotisations will be low; declaring less that you earned one quarter and more than you earned the next, will just mean that your cotisations are out of line with what you earned. The whole point of the system is that when you earn more you can afford to pay more, and when you earn less you can pay less.