Ask HN: How much equity should give to third co-founder?

As two technical co-founders now we're looking for a new co-founder for our startup to accelerate post mvp sales process. Since we're lacking skills and also time wise it's not efficient to work on something you're not expert, mostly we focus more on product development and customer onboarding/support since now. So what do you think as in equity split, what's fair for us, new joiner and also potential future investors? A bit on current state of startup: It's on MVP stage B2B SaaS company. We have one active customer which is paying around 400usd / month. We're working on it as side gig since last 2 years.