The Marco Offset

This is the repository for the website TheMarcoOffset, a calculator to figure out your Marco Offset amount.

What is The Marco Offset?

The Marco Offset is a way to calculate your minimum donation to Relay for the St. Jude fundraiser based on a method devised by Marco Arment on the Accidental Tech Podcast.

To calculate:

1. Subtract the base model price of the Apple devices you are purchasing from your total purchase price.
2. The difference is your minimum donation.

Include in your total purchase price:

• Phone upgrades (storage, size, etc.)
• Accessories
• AppleCare (monthly cost multiplied by 12)
• Taxes
• Shipping costs

The three levels

As of ATP 707, the offset has three levels. Pick whichever one you can swing:

Level	Formula
1 — Base Offset	total purchase − base price (the original offset, unchanged)
2 — Base + Monthly AI	Level 1 + what you spent on AI this month
3 — Base + Yearly AI	Level 1 + what you spent on AI this year

Two rules apply throughout:

• Nothing goes negative. If your purchase total lands at or below base price, level 1 contributes 0 rather than a negative that would eat into the AI portion. Negative entries in any field read as 0.
• AI costs are entered in your local currency, like every other field, and are converted to USD along with the rest of the offset.

On level 3 the annual figure auto-fills as monthly × 12, and you can type over it — for a subscription plus metered usage, an annual plan, or a plan you started partway through the year. Clearing the field resumes auto-filling.

Development

The site is static: no dependencies, no package.json, no bundler. Open index.html or serve the folder with python3 -m http.server. The only build step is a rate refresh, described below.

The offset arithmetic lives in assets/js/calculator.js as pure functions with no DOM access, so it is testable directly. assets/js/script.js handles the page wiring and calls into it.

node --test

Netlify runs that same command on every deploy (see netlify.toml), so a failing test blocks the deploy.

Conversion rates

Rates come from Frankfurter, pinned to the ECB's daily reference fixing, and reach the page two ways:

• scripts/fetch-rates.js rewrites data/conversionRate.json before each Netlify build. A Frankfurter outage is not a build failure — the script warns and leaves the committed rates, which node --test then validates.
• The page fetches today's fixing directly and upgrades the rate once it lands. This never blocks the first render, and any failure leaves the committed rates in place.

There is no scheduled refresh build: Netlify's free tier allows about twenty builds a month, and a week-old rate is only ~0.5% off. Run node scripts/fetch-rates.js to refresh the file by hand.

Both paths share ratesUrl() and ratesByCountry() in assets/js/calculator.js, and derive the quote currencies from data/devices.json. Adding a country is described in CONTRIBUTING.md.

Enhancements to Add

• Multi-country support: Expand the functionality to support different currencies. Thinking best to probably add Canada, GBR, and the Euro. Github Issue
• Additional Apple products: Support for calculating donations based on the purchase of other Apple products such as Apple Watch, AirPods, etc.
• Product selection checkboxes: Replace the current dropdown of iPhone models with checkboxes for multiple product types (e.g., iPhone, Watch, AirPods) to allow users to select multiple products.

How to Contribute

1. Fork the repository.
2. Create a new branch.
3. Make your changes and submit a pull request.

Adding a country or currency has a specific order to it — see CONTRIBUTING.md.

Change Log

2026-09-08: Added the three offset levels from ATP 707 (base, plus monthly AI cost, plus annual AI cost). Extracted the offset math into assets/js/calculator.js and covered it with node --test.
2025-09-10: Redesign of website to now make it a calculator of all products released in the September Apple event. Add the ability to select countries. To start added USA, Canada, UK, and Italy.
2025-09-09: Updated to 2025 campaign and iPhone release information; Added functionality where the sub-campaign link auto passes along your suggested minimum donation as a parameter
2024-09-12: Updated to 2025 campaign and iPhone release information.
2023-09-18: Rename "Apple Care" to "AppleCare"
2023-09-15: Corrected typo
2023-09-13: Sub-campaign added to the page
2023-09-12: Inital commit; added Pico CSS; Fixed decimal formatting of minimum donation