How to Build a Credit Billing System with 500% Margin Using Stripe

#stripe #saas #webdev #startup

How to Build a Credit Billing System with 500% Margin

The Business Model

At LeadHunting AI, I needed a billing system where admin uses AI tools for $0 (Google AI Studio free tier) and users pay credits for AI generation at 500%+ margin.

Credit Packs

Users purchase credit packs:

25 credits for $1
100 credits for $3
500 credits for $10
1,000 credits for $18
5,000 credits for $75
25,000 credits for $250

Stripe Dynamic Pricing

Instead of creating products in Stripe, I use price_data:

const session = await stripe.checkout.sessions.create({
  mode: 'payment',
  line_items: [{
    price_data: {
      currency: 'usd',
      product_data: { name: '100 AI Credits' },
      unit_amount: 300, // $3.00
    },
    quantity: 1,
  }],
  metadata: { userId, credits: 100 },
});

No product management needed. Just dynamic pricing.

Atomic Credit Deduction

Credits are deducted BEFORE generation (pre-pay model):

Check user exists and is active
Check daily limit not exceeded
Check sufficient balance
Atomically decrement creditBalance
Create Transaction record
Create UsageEvent for tracking

All in one DB transaction — no race conditions.

Auto-Refund on Failure

If AI generation fails (e.g., API error), credits are auto-refunded:

try {
  const result = await generateContent();
  return result;
} catch (err) {
  await refundCredits(transactionId, err.message);
  throw err;
}

The Math (500%+ Margin)

Category	Cost	User Pays	Profit	Markup
Text (2K tokens)	$0.0006	$0.02	$0.0194	3,233%
Image (1)	$0.04	$0.30	$0.26	650%
Video (8s)	$2.80	$16.80	$14.00	500%
Audio (3K chars)	$0.048	$0.30	$0.252	525%

Admin Cost: $0

Admin uses Google AI Studio free tier (1,500 req/day). No cost.

Try It

Originally published on leadhunting.app

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