The arithmetic nobody does before subscribing

The two models

Subscription. A monthly fee buys a credit allowance at a lower effective price per second. Unused credits generally expire at the end of the period; where they roll over, it is usually capped and usually only while you remain subscribed.

Pay-as-you-go top-up. You buy credits when you need them, at a higher price per second. Most top-up credits do not expire, or expire over a much longer horizon. Available directly and through aggregators such as fal.ai and Replicate.

Doing the sum

The question is not which is cheaper per second. It is which is cheaper for how you actually work.

Work out three numbers:

1. Your monthly usage in seconds of generation, from your last two real projects. Not your optimistic estimate.
2. The subscription’s effective price per second, which is the monthly fee divided by the credits it includes, converted into seconds at your usual model and resolution.
3. The top-up price per second for the same model and resolution.

Then: subscription cost per month against top-up price times your actual usage.

The result surprises people, because the comparison people run in their head is the subscription’s price per second against the top-up’s, which ignores that the subscription charges you whether you generate or not.

Irregular work changes the answer completely

For a student, a freelancer with uneven months, or anyone learning, the pattern is usually: three weeks of nothing, one intense week, then nothing again.

A subscription over that pattern pays full price for the quiet months and expires unused credits in them. Top-up costs more per second during the intense week and nothing at all otherwise, and over a year it is frequently cheaper in total.

The honest general advice: if your work is irregular, top up. If you generate every week, price the subscription against your real usage and subscribe only if the sum works.

What to read before subscribing

Four clauses, and they are not always on the pricing page:

• Rollover. Do unused credits carry over, and is there a cap?
• What happens on cancellation. Do remaining credits survive, and for how long?
• Commercial-use rights. Are they tied to the tier? Some services grant commercial rights only above a certain plan, which matters enormously if you are billing a client.
• Queue priority and resolution limits. Free and low tiers are often capped at lower resolutions or slower queues, which affects whether the plan can actually do your work.

Screenshot what the terms said on the day you subscribed. Terms change, and a dispute is much easier with a record.

Aggregators: the margin and what it buys

fal.ai, Replicate and consumer aggregators resell access to several underlying models. You pay a margin over the model’s own price.

What the margin buys is real: one balance instead of six, one interface, the ability to switch models without opening new accounts, and no monthly commitment. For someone testing several models, or working irregularly, that is often worth more than the margin costs.

What it costs, besides money, is one more step of distance from the model’s own controls, and a dependency on a company that is not the one building the model.

The number to write on paper

Whatever you choose, do this once: work out what a single eight-second generation at your working resolution costs in your own currency. Write it on paper and put it next to the screen.

Credits exist to put distance between the click and the cost. Closing that distance manually changes behaviour more than any budgeting advice, and it takes five minutes.

Then multiply by your measured takes-per-shot from the continuity module. That product is your real cost per delivered shot, and it is the number a quote has to be built on.

The free path, and its real cost

Free daily allowances, Hugging Face Spaces and Colab or Kaggle sessions cost nothing in money and cost queue time and session limits. A free session that dies at eighty per cent through a render is a real loss of an hour.

Use them without hesitation for learning and for your own work. Do not promise a client a deadline that depends on somebody else’s free queue.

Today: work out your cost per eight-second generation in your own currency, multiply by your takes-per-shot, and write both numbers where you will see them.