What the agent did
He could not work out the sell-and-buy cash flow in Excel, so he built a calculator with Claude Code, mostly from his phone. It shows BSD, CPF refund, SSD, mortgage stress tests and a month-by-month timeline on one screen. He published it as open source.
Result, as claimed
"Built a Singapore property upgrade calculator, mostly on my phone, with Claude Code." He notes it gives estimates only.
This is the result as the person described it in public. It has not been checked and is not a typical outcome.
Proof
Try it yourself
Build a simple personal calculator with a coding agent for a money decision your spreadsheet cannot handle.
Prompt
Help me build a simple web calculator for [decision, for example selling my flat and buying a condo in Singapore]. Inputs: [sale price, outstanding loan, CPF used plus accrued interest, purchase price, loan amount, interest rate]. Calculate [buyer's stamp duty, CPF refund, seller's stamp duty if any, monthly mortgage with a stress test at a higher rate] and show a month-by-month cash flow timeline. Use the official rate tables I give you [paste or link]. Label every result as an estimate.Tools
- Claude Code What Mingming Wang used
- His calculator Open-source example to look at first
- IRAS Official stamp duty rates in Singapore
- CPF Board Official CPF refund rules
Steps
- Write down your inputs and the result you need.
- Get the official rates from the government sites.
- Ask the agent to build it and test it on numbers you have worked out by hand.
- Use it for planning only.
Watch out: Rates and rules change, so check results against official calculators or a professional before making a property decision.
Starter version by Solopreneur Code