Forbes asks the company, and they guess if the company doesn't share. If the company does share, the numbers are not AFAIK audited. (This is to say that I would not expect the Forbes data to be especially accurate.)
Basecamp is claiming 200k more accounts since 2018. At 100% retention, that's $20mm per month of new revenue. Factor in whatever churn you want, a $25mm annual revenue estimate for Basecamp 2017 sounds ridiculously low. (They are claiming 700k new accounts between 2016 & 2018.)
Right, take the $20mm/mo in gross new business & apply your favorite convert rate to that. Then, apply your favorite churn rate to the existing business.
You have to pick really pessimistic numbers to get from 2.8mm signups of a $99/mo service to arrive at a $25mm annual revenue number. Specifically: ~.75% of their total claimed signups since 2004. Or ~2.5% of their claimed signups since 2016.
(Put another way: if they converted 10% of their signups since 2016, that's > $100mm run rate before accounting for churn.)
Basically, to assume they are doing only $25mm annually you have to assume either (as the parallel comment does) they are publicly lying about their number of signups or that they have pretty poor conversion/retention numbers. My guess is option #3: they are doing much more than $25mm annually.
I've also seen that figure thrown around quite a bit and I'm a bit skeptical. It also makes the question of profit redistribution particularly interesting given the tone DHH employs everywhere.
Basecamp is claiming 200k more accounts since 2018. At 100% retention, that's $20mm per month of new revenue. Factor in whatever churn you want, a $25mm annual revenue estimate for Basecamp 2017 sounds ridiculously low. (They are claiming 700k new accounts between 2016 & 2018.)