Opportunity Cost App: A Browser Extension That Converts Every Price You See Into Bitcoin

Every price tag you encounter online—whether it's a $47 Amazon purchase, a $650,000 Zillow listing, or a $4.50 latte on a café menu—represents a choice. Buy this thing, or hold onto money that might be worth more tomorrow. For most of human history, inflation made that calculus simple: spend now, because your dollars will buy less next year.

Bitcoin inverts this logic. And a free browser extension called Opportunity Cost, launched in June 2025 by TFTC (the media company founded by Marty Bent), wants to make that inversion impossible to ignore.

What the Extension Actually Does

Opportunity Cost scans every webpage you visit, identifies prices in over 10 fiat currencies (USD, EUR, GBP, JPY, CNY, and others), and overlays their Bitcoin or satoshi equivalents in real-time. That $1,200 laptop becomes 0.012 BTC. The $35 book becomes 35,000 sats.

The technical implementation is straightforward: the extension uses a MutationObserver to detect dynamic content changes (like prices loading on Amazon or banking apps), fetches BTC exchange rates from APIs roughly every 30 seconds, and processes all conversions locally in your browser. No accounts, no data collection, no tracking.

You can configure it to show dual prices (fiat alongside Bitcoin), Bitcoin-only mode, toggle between BTC and satoshis, enable dark mode, or disable it for specific sites. Version 0.0.5 works on Chrome, Brave, and Firefox.

The Psychological Reframe

The stated mission is helping users understand "the true cost" of spending fiat. This framing deserves unpacking.

In traditional finance, opportunity cost means what you give up by choosing one option over another. When you spend $100 on dinner, you're not just losing $100—you're losing whatever else that $100 could have become. In an inflationary fiat system, holding cash guarantees loss of purchasing power, which makes spending rational.

Bitcoin, with its fixed supply of 21 million coins, creates the opposite pressure. If you believe BTC will appreciate against fiat over time, every purchase carries a steeper opportunity cost. That $100 dinner isn't just $100—it's the 10,000 sats that might buy dinner for four in a decade.

Marty Bent describes this as restoring a "proper hurdle rate" for spending decisions—a concept borrowed from corporate finance, where it represents the minimum return an investment must generate to be worthwhile. Fiat inflation, in this view, artificially lowers that hurdle rate, encouraging consumption over saving.

Who This Is Actually For

The extension targets two audiences that don't usually overlap.

For Bitcoin newcomers, it's a frictionless introduction. No wallet setup, no exchange accounts, no buying required. Just install and suddenly every price online gets translated into an alternative unit of account. The idea is building "Bitcoin intuition" through constant, passive exposure.

For longtime holders, it's a spending gut-check. Even people who intellectually understand Bitcoin's value proposition can lose sight of opportunity costs when prices appear only in dollars. Seeing that a new TV costs 0.05 BTC reframes the decision.

The extension has found traction in Bitcoin circles—the GitHub repository (MIT licensed, open source) has 52 stars and 9 forks, with contributions from developers Moses Finlay and Brett Morrison. Screenshots of converted prices have become shareable content on X, extending the tool's reach beyond active users.

Limitations Worth Acknowledging

A few caveats for anyone considering installation:

It's a one-way conversion. The extension assumes BTC appreciation, but Bitcoin's price in fiat has historically been volatile. The 0.012 BTC laptop today was 0.024 BTC six months ago and might be 0.008 BTC next quarter. The tool doesn't show you this context.

Adoption is inherently limited. Browser extensions reach a self-selecting audience of people who already care about Bitcoin enough to install one. It's unlikely to shift behavior for the broader population who never encounters it.

It optimizes for one mental model. The "opportunity cost" framing treats holding BTC as the default best choice. That's a perspective, not a universal truth. People have rent to pay, medical bills, children to feed. A tool that makes every purchase feel like a loss might not produce healthy financial psychology for everyone.

No download metrics are public. Despite positive community reception, there's no data on actual usage numbers, making it hard to assess real-world impact.

The Broader Context

Opportunity Cost isn't the first Bitcoin pricing tool—manual calculators like bitcoinopportunitycost.com have existed since 2021. What's different is the passive, always-on approach. You don't visit a website to calculate; you simply browse the internet and see Bitcoin prices everywhere.

TFTC built the initial prototype using AI-assisted development (ChatGPT, Replit), which explains the rapid launch. The company has explored potential monetization paths, though details are sparse and any revenue model would need to preserve the privacy-first design to maintain credibility.

For Bitcoiners, the extension is a small but useful tool for maintaining what its creators call "low time preference"—the discipline of delaying gratification for long-term gain. For skeptics, it's a curious experiment in behavioral economics, testing whether constant price translation actually changes spending habits or just creates decision fatigue.

The honest assessment: if you already think in Bitcoin terms, this automates something you're doing manually. If you don't, installing it won't magically convert you—but it might plant seeds. Whether those seeds grow into genuine financial discipline or just another browser extension you forget about depends entirely on what you do with the information.