By default, the host organization that collects money on behalf of the collectives takes a 5% commission (on top of the classic 5% commission for the crowdfunding platform and the credit card fees which are 1.4% + €0.25/transaction for European cards).

Such commission exists because the host organization (BrusselsTogether ASBL in this case) is taking care of the bookkeeping and filing annual tax reports to the government so that individual collectives don't have to (we have been quoted €2-3k for the first year by our accountant in Brussels).

So the benefit for the collectives is clear: instead of having to create your own non profit and pay for an accountant, you can use BrusselsTogether ASBL for a 5% commission.

Now, some hosts ask more than 5% (e.g. Women Who Code 501(c)(3) asks for 10%). The reason being that they offer more than just accounting, they also promote the brand and offer a free subscription to meetup.com to all their collectives (local chapters).

Another way to look at it is that all the collectives operating under the #BrusselsTogether umbrella, agree to put 5% of their budget together to cover expenses that can be mutualized (and hence be cheaper). It's important to note that BrusselsTogether is operating as an open collective itself so everyone can see how much money we have and anyone can suggest how we should spend the money.

My recommendation is to go with the default 5% and we can always revisit this in the future as we will have more data and more feedback from actual collectives.