How we calculate
Every number on this site comes from a formula and a data source, not a guess. Here's exactly how the tools work, where the figures come from, and — just as importantly — what they can and can't tell you.
Our approach
Three principles shape every calculator here. First, real-world data over lab figures: we use the capacity and consumption numbers cars actually show, not the ideal EPA or WLTP ratings. Second, transparency: the maths below is the same maths the tools run, and the data sources are named so you can check them. Third, honesty about the limits — these are well-grounded estimates, and where the data thins out we say so rather than inventing precision.
How the battery health check works
The battery health calculator doesn't need a diagnostics tool — it works from three numbers your Tesla already shows in its Energy app: your average energy consumption (in Wh per mile or km), the projected range it estimates at your current charge, and your current battery percentage. From those it works backwards to your pack's real usable capacity:
- Energy available now = average consumption × projected range. (e.g. 250 Wh/mi × 200 mi = 50 kWh)
- Full usable capacity = that energy ÷ current charge %. (e.g. 50 kWh at 80% → 62.5 kWh)
- Battery health = your full usable capacity ÷ the original usable capacity for your exact model, year and trim. (e.g. 62.5 ÷ 75 ≈ 83%)
The original-capacity figure in step 3 comes from our per-variant capacity table (below), which is why picking the right trim and year matters for an accurate result.
Where the capacity figures come from
Every model and trim has its own usable (not gross) capacity figure — the energy you can actually use, which is what the car works from, rather than the larger total pack size. These are compiled from Tesla's published specifications and measured usable figures reported across the fleet, then maintained per model year and trim. You can see the full tables on the battery specs & facts page and on each model battery-health page. Capacity can vary slightly by market, software version and production batch, so we treat these as close reference points rather than exact constants.
How the degradation curves are built
When you compare your result against a curve, you're comparing it to a fleet average — the typical capacity retention at a given mileage for your model and chemistry. Those benchmarks are compiled from aggregated real-world fleet data, primarily Tessie's public fleet statistics, and supplemented by documented owner reports and InsideEVs long-term case studies where the fleet sample is still thin (the LFP Model 3, for example). The curve interpolates between real data points, and we're explicit about confidence:
- Each curve is drawn as a solid line only as far as the data is reliable — roughly 150,000–200,000 miles for the Model S, X, 3 and Y nickel packs.
- Beyond that point it switches to a dashed line to show the figures are extrapolated, not measured.
- Where there genuinely isn't enough data yet — the Model Y LFP pack and the Cybertruck — we don't show a curve at all rather than guess.
How the other tools calculate
Warranty checker
Applies Tesla's 8-year battery and drive-unit terms with the model-specific mileage caps (100,000 / 120,000 / 150,000 miles) and the 70% capacity-retention guarantee, ending cover at whichever limit — years or miles — you reach first.
Cost calculator
Cost per mile is simply your energy consumption multiplied by your price per kWh; total journey cost is that figure times distance. It uses your own consumption and tariff, with regional rate guides for home, Supercharger and public charging as a sanity check.
Charge time calculator
Energy needed is the gap between your start and target percentages applied to your pack's usable capacity; time is that energy divided by charging power. AC speeds are capped at the car's onboard-charger limit, and DC charging models the way power tapers as the battery fills past ~80%.
Range estimator & route planner
Start from real-world consumption baselines, then adjust for cruising speed, outside temperature, climate-control load, terrain and weight. The route planner adds each Supercharger's peak power and the charging curve to estimate stop locations and durations.
Value estimator
Combines model-and-trim depreciation patterns with mileage and your measured battery health, since a healthier pack supports a stronger resale value.
What these numbers are — and aren't
Everything here is an estimate, not a factory diagnostic. The battery health figure depends on the accuracy of the numbers your car reports and is best read as "healthy, average, or worth a closer look" rather than a certified percentage. Fleet averages describe the typical car, not yours specifically — climate, charging habits and use all create spread around the line. For anything that really matters, treat these as a well-informed starting point and confirm with a Tesla service-centre reading. If you ever spot a figure that looks wrong, please tell us — corrections from real owners are how the data improves.
Sources
- Tessie fleet statistics — aggregated real-world capacity-retention data
- InsideEVs long-term battery case studies and documented owner reports
- Tesla's published vehicle specifications and owner's manual charging guidance
- Further charging and longevity references are cited on the maximising battery life guide