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Hey, it’s Jeffrey — I was recently on the Catching Up to FI podcast talking about exactly this kind of thing, and this week's issue is a little different.
No spreadsheet, no account login, no digging through old statements. Just a prompt that builds something.
I love spreadsheets. But most people don't — and even those who do know that building a good one for their finances takes time. What if you could skip that entirely and have Claude build you an interactive version in about 30 seconds? No formulas, no formatting, no cell references. Just describe what you want, and it appears.
That's what this prompt does. It builds a working, interactive calculator — with dropdowns, live-updating results, and a slider — that runs right inside Claude. No coding. No app. No spreadsheet required.
I built one around a concept I think about a lot for this newsletter: the real dollar cost of financial procrastination. Most of us have something we've been putting off. Switching to a better savings account. Investing cash that's been sitting idle. Rolling over an old 401k. The task isn't hard — I just never got around to it.
This calculator puts a number on that delay. By the day. Compounded monthly. With editorial commentary that gets less polite the longer you've been waiting.
Run it on your own scenario first. Then scroll down to see what mine showed.
Build me an interactive "Procrastination Tax Calculator" that runs right here in our conversation. It should calculate the real dollar cost of delaying a financial task.
Include these scenarios as dropdown options, each with its own math:
1. Switching to a higher-yield savings account — compare APY difference on a balance over time delayed (inputs: current balance, current APY, target APY)
2. Rolling over an old 401k — estimate drag from higher expense ratios during delay, assuming 8% underlying growth (inputs: balance, current ER, rollover ER)
3. Paying off a credit card — interest accrued during delay period (inputs: balance, APR)
4. Investing a cash lump sum sitting idle — opportunity cost vs expected return (inputs: amount, expected annual return defaulting to 10%)
5. Custom scenario — open-ended with fields for amount, annual rate, and an optional description
Include a delay slider from 1 to 36 months.
No button. Results should calculate and appear automatically as soon as valid inputs are entered, and update live as the user types or adjusts the slider.
For every scenario, show:
* Total cost of procrastinating (big, prominent number)
* Daily cost ("$X/day")
* Time wasted
* A short, slightly roast-y editorial line that changes based on how long they waited — gentle and encouraging under 3 months, increasingly savage after that. Include at least 5 lines per tier. Only change the roast when the user crosses into a new tier, not on every slider tick.
All math should compound monthly. All dollar outputs should be rounded and formatted with commas.
Design: clean, not corporate. A little personality. Should feel fun to use, not like a bank website.
Run it now → Claude
What I got when I tested it:
I ran two scenarios just to see it in action.
First: $15,000 in a savings account earning 1% APY, with a 3.5% APY account available. Six months of delay: $189. That's $1.04 a day.
Second: $20,000 in idle cash, not invested, at a 7% expected return. Also six months: $710. That's $3.89 a day.
The calculator’s line at the six-month mark: "You've now spent more on procrastination than most people spend on coffee. Monthly."
A couple of things worth noting. The math here is illustrative. I didn't spend time stress-testing it for precision, and if you want to use this seriously, I'd refine the prompt with your own assumptions and more closely check the math behind the calculations.
But that's actually the whole point: this is your calculator. Swap in any scenario, adjust the inputs, make it yours. And it doesn't have to be a procrastination calculator — you could describe almost any calculation you've wanted a clean, interactive tool for, and Claude will build it. No coding, no spreadsheet, no app required.
Keep going? Once the calculator is built, try these follow-ups:
"Add a new scenario for [describe it] — same design, same live updating, same roast line logic."
"Change the color scheme to something darker and more minimal."
"Add a results history so I can see all the scenarios I've run in one place."
"Export a summary of my results as a table I can copy and paste."
AI tip worth trying this week
Something I've been doing that saves more time than I expected: instead of manually hunting through a webpage, email, or document to make edits, I paste the whole thing into Claude and just describe what I want changed. "Move the second paragraph up, update the fee to $127, replace the title with this." It spits back the full updated version instantly. Works especially well when your boss or a client sends you a list of changes — just paste the document and the list, and let Claude do the tedious part.
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One quick note: This newsletter is for educational purposes only and does not constitute financial advice. I'm not a financial advisor — just someone sharing ideas and tools I've found useful. Use what works for you, skip what doesn't, and always do your own research. Some links may be affiliate links or sponsored content for which I may receive compensation.