https://www.hatch.org/categories/math/ Recent content in Math on Steve Hatch's Blog Hugo en-us Sat, 03 Oct 2026 00:00:00 +0000 https://www.hatch.org/2026/10/03/27-dollars-a-day/ Sat, 03 Oct 2026 00:00:00 +0000 https://www.hatch.org/2026/10/03/27-dollars-a-day/ <p><img src="https://www.hatch.org/images/27-dollars-a-day.png" alt="$27.40 a Day: The Boring Math That Turns Into Half a Million Dollars"></p> <p><strong>The most powerful number in personal finance isn&rsquo;t a stock tip. It&rsquo;s $27.40.</strong></p> <p>That&rsquo;s what you get when you divide $10,000 by 365. One lunch out and a coffee. A couple of streaming subscriptions and a delivery fee. The kind of money that leaks out of a normal day without anyone noticing it&rsquo;s gone.</p> <p>A few months ago I built a <a href="https://www.hatch.org/compound/">little compound interest calculator</a> to teach my 20-year-old sons about compound interest. I wanted them to <em>see</em> the curve instead of just hearing me talk about it. It worked well enough that I wanted to share it further. The thing that keeps grabbing me is how absurd the gap is between how small the daily number feels and how big the 20-year number gets.</p>