sdlt-calculator

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 Models frequently use outdated rates (e.g. old £625,000 FTB cap, old band thresholds)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:

# Standard purchase
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 350000

# First-time buyer
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 450000 --ftb

# Buy-to-let (additional property, non-resident)
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 500000 --additional --non-resident

# Compare all scenarios
bash {{SKILL_DIR}}/scripts/sdlt-calc.sh 300000 --compare