How to Handle User Authentication and Payments for Free on Day One

Login and payments are the two parts of a product you should never build yourself. They are also the two parts people overpay for early. The good news is that both can cost $0 on launch day. Login tools charge by active users, so a new app pays nothing. Payment tools charge a cut per sale, so you only pay when you earn.

Here is how to set up each side, and where the quiet costs are.

Part 1: Login that costs nothing

Clerk

The first 50,000 monthly retained users per app are free, with no card, 3 dashboard seats, a custom domain and most authentication features. Past 50,000 you move to Pro, with overage from $0.02 per user a month. Organizations are free up to 100, and past that you add the B2B Authentication add on. Reviewers warn that cost climbs at higher volumes. See Clerk or visit clerk.com.

WorkOS AuthKit

The first 1 million monthly active users are free, and no card is needed until production. The catch is polish: a custom domain costs $99 a month and custom branding is an extra fee, so a fully branded login page is not free. Single sign on is $125 per connection. See WorkOS AuthKit or visit workos.com.

Firebase Authentication

50,000 monthly active users on the no cost Spark plan, with no payment method. Phone sign in is not available on Spark, because SMS is billed per message on the Blaze plan. Daily email caps are low: 150 password reset emails and 5 email link sign in emails a day. See Firebase Authentication or visit firebase.google.com.

Supabase

The Free plan includes 50,000 monthly active users alongside a 500 MB database and 1 GB of file storage, for up to 2 active projects. Free projects pause after one week of inactivity, so a quiet side project will go to sleep. See Supabase or visit supabase.com.

Part 2: Payments with no monthly fee

None of these have a free transaction allowance. They are free to start, and you pay a fee on each sale. So compare them on a small sale, because the fixed part of the fee hurts most there. On a $5 sale, Stripe's 2.9% plus 30 cents is about 44 cents. Paddle, Lemon Squeezy and Polar Starter charge 5% plus 50 cents, which is 75 cents, or 15 percent.

Stripe

2.9% plus 30 cents per successful card payment, with extra for manually entered cards (0.5%), international cards (1.5%) and currency conversion (1%). Disputes cost $15 each. Stripe Billing starts at $620 a month and Tax at $90 a month on annual contracts, so add those only when you need them. G2 lists fees as the top drawback. Stripe is not available in every country, so check the supported list before you plan around it. See Stripe or visit stripe.com.

Polar

The Starter plan is free with a 5% plus 50 cents fee, plus 1.5% on international cards and payout fees of $2 a month of active payouts plus 0.25% and 25 cents per payout. Pro is $20 a month at 3.8% plus 40 cents, so it pays for itself somewhere between roughly $600 and $1,500 of monthly sales, depending on your price. Trustpilot shows 1.8 stars from 23 reviews. See Polar or visit polar.sh.

Paddle

5% plus 50 cents per checkout transaction, with global tax and regulatory compliance, fraud protection, chargebacks and buyer support in the price. You hand off sales tax instead of filing it yourself. G2 reviewers mention slow support. See Paddle or visit paddle.com.

Lemon Squeezy

Also 5% plus 50 cents, with automated sales tax compliance and fraud protection, plus email marketing free up to 500 subscribers. Trustpilot shows 1.2 stars from 183 reviews, with complaints about slow, unhelpful support. Read recent reviews before you commit. See Lemon Squeezy or visit lemonsqueezy.com.

A setup that works on day one

• Login: Clerk or Supabase, whichever matches your database.
• Payments, if you sell worldwide and hate tax paperwork: Paddle or Polar.
• Payments, if you want the lowest fee and Stripe supports your country: Stripe.

Before launch, run one real payment with your own card and refund it. Then log in on a second device and reset your password. Those two checks catch most of what breaks on day one.