The benchmark for a company raising its Series A is now $50k MRR. (This used to be closer to $100k.) You'd expect to be at $100–150k MRR six months after the Series A, assuming a 15–20% monthly growth rate.
If you're already at $500k MRR, you're in Series B territory.
While the bar for absolute revenue may be lower, the growth rates of the best SaaS companies are astonishingly higher. The markets are bigger now, so your growth from $1–2m ARR to $10m ARR and beyond has to be much faster these days.
If you're already at $500k MRR, you're in Series B territory.