/ the average hides it

One plan, three kinds of user

Free AI pricing calculators take one average cost per user and one plan. Averages hide the problem: the heavy users. Undertow shows every plan at typical, heavy and extreme usage, the usage at which a user stops paying for themselves, and the price, cap or model change that fixes it — saved between visits.

PLAN PRO · $12/MONTH · NO LIMITPROFIT PER USER / MONTH

+$5.22

−$1.94

−$20.39

−$61.12

Typical300 req · 80%

All usersthe average

Heavy2,500 req · 15%

Extreme6,000 req · 5%

Pro earns $5.22 on a typical user and loses $20.39 on a heavy one.

A request costs $0.0116 (Claude Sonnet 5.5, 10% Opus 5.5). The average across Pro users looks like a small loss; the heavy users are where the money goes.

748requests a month — the point where a Pro user starts costing more than they pay

/ margin grid by plan and usage

Every plan, every kind of user

Up to four plans × typical, heavy and extreme users: margin and profit per user, the margin across all users, and the requests per month at which a user starts costing more than they pay. Coloured against your target margin, with a one-line verdict on top.

Plan	Typical user	Heavy user	Extreme user	All users	Loses money above
Freecapped at 50 requests	−$0.4740 req · cost	−$0.5850 req · cost	−$0.5850 req · cost	−$0.49per free user	free plan
Pro$12.00/mo · no limit	43%$5.22 · 300 req	−170%−$20.39 · 2,500 req	−509%−$61.12 · 6,000 req	−16%−$1.94 per user	748requests / month
Team$30.00/seat · 2,000 incl., then $1.50/100	64%$19.20 · 600 req	13%$5.84 · 3,000 req	17%$20.47 · 8,000 req	47%$17.26 per user	neveroverage covers it

Undertow’s built-in example · target margin 70% · card fees 2.9% + $0.30 · 5 free users per paying user. With 800 Pro and 150 Team users: 160 of 950 paying users cost more than they pay.

/ fixes that solve for your target margin

Three ways out, each with its number

For each paid plan, worked out for a heavy user: the price that reaches your target (and the price to break even), the monthly cap that holds it at today’s price and which users would hit it, and the share of requests to move to a cheaper model.

01 · price

Raise Team’s price

$124.70

a month per seat reaches 70% on a heavy Team user (from $30.00).

Pro would need $118.23 — or $33.00 just to break even on a heavy user.

02 · cap

Cap Team’s usage

446

requests a month holds 70% at today’s $30 — all three groups would hit it.

A cap trades margin for what your users can do: the grid shows who it touches.

03 · model

Route to a cheaper model

95%

of Claude Sonnet 5.5 requests moved to Claude Haiku 5.5 brings a heavy Team user to 70%.

For Pro, even 100% isn’t enough on its own — Undertow says so.

/ how it works

Describe one request, then your plans

Undertow Setup: request shape presets, main model Claude Sonnet 5.5, 3,000 input tokens, 60% cached, 800 output tokens, cost per request $0.0116

On Setup, describe one request: the model, input and output tokens, cache share and model calls.
Add your plans: price, usage limit, and how many requests typical, heavy and extreme users make.
Open Margins: read each plan’s margin per user group and the usage at which users stop paying for themselves.
Drag the levers or apply a fix — price, cap or a cheaper model — and watch every plan update.

/ what’s inside

Built for how AI plans really work

Usage limits as they really work

No limit, a hard cap, or included requests with overage billed per 100 requests. Free plans are costed too, and their model cost is shared across paying users.

Testing whether an overage price covers heavy users, or whether a free tier is eating the paid plans’ margin.

Levers and a usage chart

Drag cache share, output length, model mix, a model price change or your target margin, or edit a plan’s price or cap — every plan updates. A chart shows profit per user as usage grows, with the break-even point and each user group.

Seeing how much a better cache hit rate or shorter answers is worth before building it.

Real usage from an export

Paste user ; plan ; requests for a month: per plan, the median, 90th and 99th percentile, and the averages of the bottom 80%, next 15% and top 5% — applied to a plan in one click.

Replacing guesses with your actual heavy users once you have customers.

Dated, editable model prices

17 current text models from Anthropic, OpenAI and Google, from their official pricing pages checked on 13 October 2026, with long-prompt rates applied automatically and Google’s announced 1 January 2027 prices as a scenario. Edit any price or add your own models.

Comparing Claude Sonnet 5.5, gpt-6-sol and Gemini 3.8 Flash for the same request shape.

/ real usage

Your real heavy users, from one paste

user;plan;requests
u0;Pro;120
u1;Pro;180
u2;Pro;200
… 40 lines

Plan	Users	Median	90th pct.	99th pct.	Typical avg	Heavy avg	Extreme avg
Pro	40	390	3,200	8,000	422bottom 80%	3,183next 15%	7,250top 5%

A sample paste of 40 Pro users. “Apply” copies the three groups into the plan.

/ model prices

17 models, official prices, your edits

Anthropic

Claude Fable 5.1
Claude Opus 5.5
Claude Sonnet 5.5
Claude Haiku 5.5

OpenAI

gpt-6-astra
gpt-6.1-sol
gpt-6-sol
gpt-6-luna
gpt-5.6-terra
gpt-5.4-mini
gpt-5-nano

Google

Gemini 3.8 Flash
Gemini 3.6 Flash
Gemini 3.1 Pro Preview
Gemini 2.5 Pro
Gemini 3.5 Flash-Lite
Gemini 2.5 Flash-Lite

Prices checked 13 Oct 2026

From each provider’s official pricing page. Not fetched live — the tool works offline — so every price is editable, and any other model can be added with its prices.

Scenario: Google’s announced prices for Gemini 3.8 and 3.6 Flash from 1 January 2027.

/ own vs rent

Where Undertow sits

Free to own, against usage-billing platforms that need a full billing stack and your live data.

	Undertow	Free AI pricing calculators	Usage-billing platforms (Orb, Metronome)	A chatbot
Margin per plan at typical and heavy usage	Yes — up to 4 plans × 3 user groups	One plan, one average cost per user	Simulations on your billing history	Recomputed by hand each time
Break-even usage and solved fixes	Price, cap and model routing	Break-even users only	Not a planning tool	One-off answers
Model prices	Official, dated, editable	You enter one cost	From your real usage	From memory, often older models
Works before launch	Yes	Yes	Needs live data	Yes
Account, billing stack or data connection	None	None	Required	Account
Your plans and usage data	Stay on your device	—	On the platform	Sent to the service

/ faq

Questions before you add it to your dock

Does it connect to my billing or my OpenAI / Anthropic account?

No. Undertow is a planning aid that runs offline. You describe your requests and plans (or paste a usage export), and it works out the margins. Nothing is sent anywhere.

How current are the model prices?

They were checked on 13 October 2026 on the official pricing pages of Anthropic, OpenAI and Google, and the date is shown in the tool. They aren’t fetched live — the tool works offline — so every price can be edited, and you can add your own models. We re-check them and ship updates for free.

Which models are included?

17 current text models: Claude Fable 5.1, Opus 5.5, Sonnet 5.5 and Haiku 5.5; gpt-6-astra, gpt-6.1-sol, gpt-6-sol, gpt-6-luna, gpt-5.6-terra, gpt-5.4-mini and gpt-5-nano; Gemini 3.8 Flash, 3.6 Flash, 3.1 Pro Preview, 2.5 Pro, 3.5 Flash-Lite and 2.5 Flash-Lite. Any other model can be added with its prices.

My plans use credits, not requests. Does it still work?

Yes, if one credit maps to a request of a known size: enter that request shape and treat credits as requests. Included credits become the cap or the included amount, and extra credit packs the overage price per 100.

Is the result my real API bill?

No. It is as exact as the token counts you enter. Measure your average input and output tokens in your provider’s usage dashboard and use those. Cache-write surcharges, Gemini cache storage and priority-processing premiums are not included.

What do heavy and extreme users mean?

Three groups of a plan’s users, each with its requests per month and share of users — typical is most of your users, heavy your top users, extreme the very top. With real data, Undertow builds them from your bottom 80%, next 15% and top 5%.

Do I need an account? Where does my data go?

No account, no install. Undertow is a single HTML file that runs in your browser; your plans and usage data stay on your device.

/ who it’s for

Founders and small teams selling an AI-powered product on subscription plans

Pricing a launch, adding AI features to existing plans, or re-pricing after the first model bills.

An indie founder pricing an AI writing app before launchLaunch pricing set with a fair-use cap chosen from a number, not a guess.
A SaaS team adding AI features to existing plansThe losing plan identified, with the price, cap and model-routing options side by side.
Choosing between modelsA routing decision backed by its effect on every plan.
A provider announces a price changeThe impact on each plan in seconds.

What it isn’t. Undertow is a planning aid, not billing or cost tracking. Your real bill depends on your exact token counts, so measure them in your provider’s dashboard. Cache-write surcharges, Gemini cache storage, priority-processing premiums and image, audio or embedding models are not included, and amounts are in US dollars, the currency of the model prices.

Own your tools, not a subscription

Undertow is a single HTML file. Add it to your dock, use it offline, and keep it. Prices checked 13 Oct 2026.

Get Undertow free

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