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Finance & bookkeeping · Claude

Build your own investment tracker that tells you where to put new money

Idea + starter prompt, not run by us yet

For: Long-term investors who keep their allocation rules in a spreadsheet and want an app

A Reddit poster worked out their allocation rules in Excel, then asked Claude to turn them into a phone-friendly web app. It splits monthly SIP and lump-sum money across holdings that sit below their target bands, and has a balanced mode and a correction mode. They still type in their holdings by hand. It took about a week.

Steps

  1. Write your allocation rules in a spreadsheet first: target share per holding, allowed bands and what counts as underweight.
  2. Ask Claude to build a simple web app from those rules and show you the design before it writes code.
  3. Test it with made-up holdings and compare its answers with your spreadsheet.
  4. Enter your real holdings by hand. The source did not connect to broker accounts.
  5. Keep the data on your own device and never paste account logins into the chat.
  6. Treat the output as a calculator for your own rules, not advice. Check the money split yourself before you act.

Starter prompt

Starter prompt. Change the [brackets] first.

Help me build a personal investment tracker as a simple web app that works on my laptop and phone. My rules are: [targets, bands and how to split new money].

This is a calculator only. It reads what I type in and shows numbers. It never buys, sells or moves money, and it changes nothing outside the folder [app folder].

Trial first. Build and test it with made-up holdings only, such as three fake funds with round numbers. Do not use any of my real holdings until I say so.

First show me a plan: the screens, the inputs, how you will calculate which holdings are under their target band, and how a balanced mode and a correction mode differ. Wait for my OK.

Then build it and show me a worked example I can check against my spreadsheet. When I move to real data, I will type it in by hand. Do not connect to any broker or ask for logins, account numbers or API keys. Keep the data on my device. Remind me this is a tool for my own rules, not financial advice.

Original post: Reddit · found via agentusecases.ai. Written up in our own words. We haven't run it, so test it on made-up data first.