| name | sdlt-calculator |
| title | SDLT Calculator |
| description | Calculate UK Stamp Duty Land Tax (SDLT) for residential property purchases in England and Northern Ireland. Use when asked about stamp duty, SDLT, property tax on purchase, first-time buyer relief, additional property surcharge, or non-UK resident surcharge. Handles standard purchases, first-time buyers, additional properties, and non-resident buyers. |
| author | MoverlyLtd |
| author_url | https://github.com/MoverlyLtd/conveyancing-toolkit/tree/master/sdlt-calculator |
| license | MIT |
| version | 0.1.0 |
| execution_mode | open |
| jurisdiction | gb |
| practice | real-estate |
| language | en |
SDLT Calculator
Calculate Stamp Duty Land Tax for residential property purchases in England and Northern Ireland.
Response Rules — Always Include
DO:
- Always run the calculator script — never calculate SDLT from memory or training data. The script has current rates; your training data may not.
- When FTB relief is requested for a price above the FTB cap (currently £500,000): the script will correctly apply standard rates. State clearly: "FTB relief does NOT apply because £X exceeds the £500,000 cap. Standard rates apply."
- Always quote the exact figure from the script output — do not round or recalculate
- When showing the result, include the rates source date from the script output (e.g. "Rates from: 2025-04-01")
DON'T:
- Never calculate SDLT manually — always use the script. Models frequently use outdated rates (e.g. old £625,000 FTB cap, old band thresholds)
- Don't apply FTB bands (£300,000 nil rate, £300k-£500k at 5%) when the price exceeds the FTB cap — the script handles this correctly, trust its output
- Don't override or "correct" the script's output with your own calculation
When to Use
- Buyer asks "how much stamp duty will I pay?"
- Conveyancer needs SDLT figure for a transaction
- Comparing SDLT across scenarios (first-time buyer vs not, additional property)
- Checking whether first-time buyer relief applies
How to Calculate
Run the calculator script:
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh <price> [options]
Options:
--ftb — First-time buyer relief--additional — Additional property (5% surcharge)--non-resident — Non-UK resident (2% surcharge)--compare — Show all scenarios side by side
Examples:
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 350000
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 450000 --ftb
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 500000 --additional --non-resident
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 300000 --compare
