I have been building a small set of free calculator-style websites lately, and one thing became pretty clear: simple tools are not always simple products.
The project I used for most of this learning is BizCalcKit, a free collection of calculators and templates for small business owners, freelancers, and solo operators. The tools cover things like pricing, invoices, profit margin, payment fees, sales tax estimates, quotes, and break-even math.
A few notes from the build:
1. The hard part is not the formula
Most calculator formulas are easy to find or write. The harder part is deciding what assumptions to show, what inputs to avoid, and how much explanation is enough before the page becomes noisy.
