I was migrating my SaaS from Firebase to a dedicated auth provider and almost made a $21,000/year mistake.
Here's what happened: I had 85,000 MAU and growing. Clerk's landing page looked great — beautiful pre-built components, easy integration, good docs. I was about to commit when I decided to actually calculate the cost at scale.
The Math That Changed My Mind
I built a calculator to compare every major auth provider at different scales. Here's what the numbers look like at 100K monthly active users:
ProviderFree TierCost at 100K MAUSupabase Auth50,000 MAU$25/moWorkOS1,000,000 MAU$0/moFirebase Auth50,000 MAU$275/moClerk10,000 MAU$1,825/moAuth07,500 MAU$5,000+/mo
That's a 73x price difference between Clerk and Supabase for the same core features: email/password login, social OAuth, session management, JWTs.
But Wait — Cheapest Isn't Always Best
Before you rush to Supabase, here's the nuance the pricing table doesn't show:
Clerk gives you production-ready UI components out of the box. Sign-in forms, user profile pages, organization management — all themed and responsive. If your team is small and shipping fast, the $1,825/mo might actually save you engineering time worth more than that.
Supabase Auth has no pre-built UI. You're writing every login form, every password reset flow, every MFA setup screen yourself. For a solo founder, that's 2-3 weeks of work.
WorkOS has the most generous free tier (1M MAU!) but it's designed for enterprise features — SSO, SAML, directory sync. If you just need email + Google login, it's overkill in complexity.
Auth0 is the most expensive option at scale, but it has the deepest enterprise compliance certifications. If your customers require SOC2 Type II and you need to check a box, Auth0's price includes that peace of mind.
The Decision Framework
Here's how I think about it now:
< 10K MAU: Doesn't matter, everything is free. Pick whatever has the best DX for your stack.
10K–50K MAU: This is where Clerk starts charging and the gap opens. If you're on Supabase for your database already, Auth is essentially free.
50K+ MAU: You need to do the math. $1,825/mo is $21,900/year. That's a senior developer's time for 2 months. Enough to build auth UI from scratch on Supabase.
Calculate Your Exact Number
I built a free calculator that lets you plug in your MAU and see exact costs across all providers:
👉 Auth Provider Cost Calculator
No signup, runs in your browser, data doesn't leave your machine.
What I Ended Up Choosing
I went with Supabase Auth. It took me 4 days to build the auth UI (login, signup, password reset, MFA toggle, profile page). At my current 95K MAU, I'm paying $25/mo instead of $1,825/mo. That's $21,600/year saved.
Was it the right call for everyone? No. If I had a team of 5 shipping features daily and couldn't afford 4 days on auth UI, Clerk would have been worth it. But as a solo founder, $21K buys a lot of runway.
What auth provider does your team use, and at what scale? I'm curious if these numbers match your experience.