Build a Quarterly Tax Estimator with Claude Code

Build a Quarterly Tax Estimator web app. People search for "quarterly tax estimator" about 200 times a month, plus related searches like "quarterly tax calculator", "estimated tax payments", "self employment quarterly taxes". The goal is a tool that ranks for those searches and makes money.

What it should do:
Build a quarterly tax estimator with income and deduction inputs. Calculate federal and state estimated taxes, show quarterly payment amounts and due dates. Include safe harbor calculations and penalty avoidance tips. Add payment reminders and tax calendar integration. Focus on getting accurate tax calculations working first.

How to build it:
1. Read this folder first. If it is empty, set up Next.js (App Router, TypeScript, Tailwind). Write a short PLAN.md with the pages, components, any library or API you need, and what you are leaving for later. Then build.
2. Put the tool itself on the homepage so a visitor can use it within seconds, with no sign-up. Do the processing in the browser where you can, so it is fast and cheap to run. Look at how IRS Tax Withholding Estimator, TurboTax, FreeTaxUSA do it and make ours simpler and faster.
3. Make it rank. Use "quarterly tax estimator" in the title tag, H1 and meta description. Under the tool, add a short how-to and an FAQ with FAQPage schema, and add a sitemap and robots.txt. Scaffold these programmatic pages from one template and a data file: /quarterly-tax-calculator-[state], /estimated-tax-[business-type], /quarterly-payments-[income-level].
4. Monetisation: Freemium: Basic estimates, $10/mo premium + planning tools. Add a pricing page and the free usage limit, and leave Stripe checkout as a clearly marked stub with the environment variables it needs.
5. Run it locally and test the main flow end to end, including edge cases like empty input and very large files. Fix what breaks, then finish with a summary of what works, what is stubbed and how to deploy it to Vercel.

Paste it into Claude Code in an empty folder. It plans first, so read PLAN.md and steer before it starts building.