How can self-hosting be cheaper than an API?

Self-hosted Stable Diffusion or Flux has a high fixed cost (a GPU you rent or own) but a near-zero marginal cost per image. Past a break-even volume, the flat infrastructure cost beats paying per image, which is why high-volume users self-host.

Why is Midjourney shown as a flat cost?

Midjourney sells monthly subscriptions with fast-hour or unlimited relaxed generation, not per-image pricing. So its cost per image simply falls as you generate more within a plan — the calculator divides the plan price by your volume.

Are the prices exact?

They are published list-price estimates and are labelled as such. Providers change pricing and plan structures frequently, so confirm current rates before committing at volume.

Does this include labour or prompt iteration?

No — it compares raw generation cost only. Real projects discard many drafts, so your effective cost per usable image is higher across every provider.

Image Generation Cost Calculator

Image generation cost calculator

The cheapest way to generate images depends almost entirely on volume. At a few dozen images a month, a pay-per-image API is simplest and cheapest. At thousands, a flat-rate subscription or a self-hosted GPU wins decisively. This calculator puts DALL·E 3, Midjourney, Stability AI, Flux API and self-hosted Stable Diffusion side by side at your volume and shows where the lines cross.

How the economics work

There are three pricing shapes here:

Per-image APIs (DALL·E 3, Stability, Flux) — cost scales linearly with volume. Predictable, great at low volume, expensive at scale.
Subscriptions (Midjourney) — a flat monthly fee, so cost per image keeps dropping the more you generate within the plan’s limits.
Self-hosted (SD/Flux on a rented GPU) — a fixed monthly GPU cost plus a tiny per-image electricity/compute share. A high floor, then nearly free.

The break-even point is where the self-hosted flat cost finally undercuts the per-image APIs — below it, pay per image; above it, host your own.

Tips

Account for waste. If half your generations are discarded, your true cost per usable image roughly doubles — pad your volume estimate.
Mix providers. Many teams draft on cheap self-hosted SD and only spend DALL·E or Flux Pro credits on final hero shots.
Revisit quarterly. API prices fall and GPU rental rates shift, so the break-even point moves — recalculate before renewing a plan.