Methodology & sources
Every default in our calculators is an editable estimate with a source and a check date. We don't hard-code figures that quietly go stale, and we never invent a number. All figures below were checked 2026-07-13.
How each calculator computes its answer
These aren't asserted numbers — each one is a short, published formula run against a sourced constant. The table below is the formula in one line; follow the link to the calculator itself for a full worked example with real numbers plugged in, step by step, so you can check the arithmetic yourself.
| Calculator | Formula | Full worked example |
|---|---|---|
| Referral-Savings | £ = (650 ÷ mi/kWh) × Supercharger p/kWh ÷ 100 | See the steps → |
| Charging Cost | £ = (miles ÷ mi/kWh) split home/Supercharger × each rate | See the steps → |
| Salary Sacrifice | net = sacrifice × (1 − tax% − NI%) + (P11D × BiK% × tax% ÷ 12) | See the steps → |
| Home Charger | payback = (quote − grant) ÷ [(miles ÷ mi/kWh) × rate gap ÷ 100] | See the steps → |
| Model Comparison | both models: same 8,000-mi reference → kWh → home £ → BiK £/mo | See the steps → |
| Cold-Weather Range | real range = WLTP × retained%(temp) × driving-style factor | See the steps → |
| Charge Time | time = [usable battery × (to% − from%)] ÷ effective kW | See the steps → |
Constants, sources and check dates
| Figure | Default | Source |
|---|---|---|
| Free Supercharging miles (referral) | 650 miles | Tesla UK — Refer and Earn |
| Inventory referral discount | £500 (inventory only) | Tesla UK — Refer and Earn |
| Home electricity (example default) | 24.5p/kWh | Ofgem price cap |
| EV night rate (example) | 7.5p/kWh | Typical smart EV tariff |
| Supercharger (member, peak) | 41p/kWh | Tesla Supercharging |
| Supercharger (non-member) | 53p/kWh | Tesla Supercharging |
| EV company-car BiK 2025/26 | 3% | GOV.UK company-car tax |
| EV company-car BiK 2026/27 | 4% | GOV.UK company-car tax |
| EV company-car BiK 2027/28 | 5% | GOV.UK company-car tax |
| EV chargepoint grant (max) | £350 | GOV.UK EV chargepoint grants |
| Home charger install (typical) | £800–£1500 | UK installer quotes |
Vehicle assumptions
Real-world efficiency figures are estimates from typical UK owner data and are deliberately conservative versus WLTP. Prices are indicative UK list prices — always confirm live at tesla.com/en_gb.
| Variant | Efficiency | WLTP range | Usable battery | List price |
|---|---|---|---|---|
| Model 3 (RWD) | 4.1 mi/kWh | 318 mi | 57.5 kWh | £39,990 |
| Model 3 Long Range AWD | 3.9 mi/kWh | 421 mi | 75 kWh | £44,990 |
| Model Y (RWD) | 3.7 mi/kWh | 311 mi | 60 kWh | £44,990 |
| Model Y Long Range AWD | 3.6 mi/kWh | 364 mi | 75 kWh | £51,990 |
What we deliberately exclude (because it's not true in the UK)
- No "free FSD" referral — FSD (Supervised) isn't road-legal/available in the UK yet.
- No Cybertruck referral — not sold or road-legal in the UK.
- No Tesla solar referral — Tesla doesn't retail solar panels in the UK.
- No Model S/X — removed from the UK line-up and referral programme in March 2026.