Car TCO Skill

Cars are sold on monthly payments and owned on total cost — and the two rank options differently. Depreciation (the biggest cost of a new car) never appears on a statement; maintenance (the biggest fear about an old car) is usually smaller than a year of new-car depreciation. This skill compares buy-new, buy-used, lease-forever, and keep-current on the same total-cost basis over the same horizon.

What This Skill Produces

• Ranked scenario totals — every requested scenario over the same horizon, cheapest first
• True per-month cost — total ÷ months, the number to compare against the payment the dealer quotes
• The assumption ledger — depreciation curve, maintenance ramp, insurance deltas, all labeled
• The not-modeled list — financing interest, jurisdiction taxes, reliability luck

Required Inputs

Ask for these if not provided:

• Which scenarios to compare — any of: new price, used-equivalent price, lease terms, current car's value + annual maintenance
• Horizon — years they realistically keep cars (default 8, labeled); short horizons flatter leasing, long ones flatter buying
• Miles per year and rough fuel/energy cost (defaults 12,000 mi / $0.14 per mile, labeled)

Programmatic Helper

python3 scripts/car_tco.py --new-price 38000 --used-price 24000 --lease-month 420 --keep-value 9000
python3 scripts/car_tco.py --new-price 38000 --keep-value 9000 --keep-maint 1800 --horizon 6 --json

Deterministic. Depreciation: 20% year one then 10%/yr for new, gentler for used/current. Maintenance ramps 8%/yr (used cars start further up the ramp). Leases re-lease at each term end with a fresh drive-off. Resale value is credited back — TCO is what you spent minus what you can recover.