Permit me, dear reader, the chance to dream a dream, and indulge me with a lower degree of skepticism than might be usual.

Today Giving What We Can has a bit over $0.55 billion dollars pledged, between 1450 members. They have only reported giving $10 million so far, but remember that most only joined in the last 15 months, so won't have been required to report any giving yet in order to keep the pledge.

The biggest charitable foundation in the world today is the Bill and Melinda Gates Foundation, with $42 billion in its endowment.

How long would it take us to catch them? Fortunately Giving What We Can's dashboard makes it easy to do some rough calculations.

Let's assume continued linear growth of the same kind we have had over the last 2 years. In the last 2 years people pledged an additional $400 million through Giving What We Can. At that rate, it would take another 200 years to catch up! By then we would have to have 110,000 members or so, given the amount average members expect to earn and give.

However, growth seems to be somewhat exponential. Membership grew 44% in 2013, 100% in 2014, and is on track to grow about 85% in 2015, for a (geometric) average growth rate of 75%.

Let's say this rate of growth could be maintained - how many years to catch up now? In that case it would only take 9 years.

Is this a fair comparison?

Not really. Most foundations pay out around 5% of their endowment each year, while I expect GWWC members to only pay out 3% or so. Not all will give to the best projects, though no huge foundation can spend all of their money in the best way either.

Furthermore, GWWC members will quit at some rate - though not at such a rapid rate if the idea were so mainstream that hundreds of thousands were doing it.

But if exponential growth could be maintained for just another few years, these effects would be overwhelmed a mere 2-3 years later.

Is 200,000 members impossible to imagine? It remains something just 1 in 3,500 people living in rich countries - a tiny fraction of those who are, say, vegetarian, or buy 'fair trade' goods. And the necessary number of members could be a lot lower if we manage to get just a few billionaires on board in the meantime.

What else could we accomplish with that kind of membership? At that point a significant mass political voice is possible, advocating for more and better aid, as just one of many possible examples. A big research effort to figure out where to direct the money could be funded for a pretty small share of the total money moved, if you think GiveWell doesn't already have it covered.

Do I expect this to happen? No. But I think it's at least... 5% likely within 20 years.

And I think it's a dream worth aiming for and being motivated by.

Also, read my colleague Ben's piece: Take the growth approach to evaluating start-up non-profits, not the marginal approach.