personal tax calc customgpt

As part of our CustomGPT series, I was keen to develop an AI model capable of calculating an individual’s personal tax liability using the official HMRC tax return form (we have supplied this plus much more as context in our model). The model guides users through a comprehensive set of questions to ensure all relevant information is captured for the applicable period, to generate a detailed tax computation.

4 initial prompts are provided, although you can go off script. Sit back, grab a coffee, and scroll through out screenshots mirroring a chat with the Custom GPT:

So, now you’ve had a sneak peak, here’s why I would recommend using our personal tax AI assistant:

✅ 1. Tailored Step-by-Step Guidance

Forget generic advice. This GPT walks users through the entire SA100 process, asking smart, relevant questions and matching them to the exact fields on the HMRC tax return — from income and deductions to supplementary pages and reliefs.

📊 2. Live Tax Calculations & Clarity

It calculates estimated income tax, NI, and capital gains in real time — with simple breakdowns and optional spreadsheet-style summaries. It’s like having a calculator, spreadsheet, and friendly advisor all rolled into one.

🧾 3. Handles Complex Income Sources

Whether you’re employed, self-employed, earning dividends, selling shares, or getting rental income, it keeps track of it all. It even flags when you’ll need supplementary pages like SA103 or SA108 — and explains why.

🧠 4. Explains Things in Plain English

Tax jargon? Not here. Everything is translated into plain, human-friendly language, helping users understand what they’re doing and why it matters. No more decoding HMRC notes at midnight.

🔐 5. Keeps It Safe and Legal

It never files the return for you — instead, it prepares everything you need to fill in the real HMRC form confidently and correctly. It also encourages users to consult a tax professional for anything complex.

❤️ 6. Reassuring, Friendly Tone

Let’s face it — tax returns can be intimidating. This GPT is patient, helpful, and even a bit warm, making it feel like a knowledgeable friend guiding you through the form.