Documentation
Everything you need to know to get accurate, meaningful results — including the assumptions baked in, where the numbers come from, and how to find the right inputs.
DriveCalc compares the true total cost of buying a car outright in cash versus leasing the same car over the same time period. It goes beyond the sticker price and monthly payment — factoring in depreciation, fuel, maintenance, road tax, excess mileage, and the opportunity cost of tying up your capital in a depreciating asset.
⚖️ What costs are actually being compared?
🎯 Is this a genuine like-for-like comparison?
Set the shared inputs at the top
Enter the time period (how long you'd own or lease) and your expected annual mileage. These apply equally to both scenarios and are the foundation of every calculation.
Fill in the Buy column
Enter the purchase price. Then choose your residual value method — Smart Estimate (pick the car make and its age when you buy it) or Manual (enter a value you've looked up on AutoTrader or Motorway yourself).
Add buy scenario fuel and running costs
Select fuel type, enter current price and the car's real-world efficiency. Then add annual maintenance and road tax. These costs accumulate over the full ownership period.
Fill in the Lease column
Enter the deposit, monthly payment, lease mileage allowance, and excess mileage charge from your quote. Then add the lease car's fuel details — these can be completely different from the buy car.
Set the ISA return rate
Defaults to 8% per year — a commonly cited long-run average for a diversified stock market portfolio. Adjust this to match your actual expected return, or set to 0% if the ISA scenario doesn't apply to you (see the ISA disclaimer section below).
Read the results
Results appear automatically once all required fields are filled. You'll see a full cost breakdown per scenario, total net cost, monthly equivalent cost, and a verdict showing which option wins and by how much.
Shared inputs
How long you plan to own or lease the car. This should match the lease contract length if comparing a specific deal.
Most leases are 2, 3, or 4 years. Use the same number for a fair comparison. Ownership periods beyond 5 years tend to favour buying significantly.
How many miles you expect to drive per year. Affects fuel cost in both scenarios and excess mileage charges in the lease scenario.
Check your current odometer vs 12 months ago for an accurate figure. UK average is around 7,400 miles per year. Be honest — overestimating your lease allowance leads to expensive excess mileage bills.
Buy scenario
The price you'd actually pay for the car — on-the-road (OTR) price including delivery, first registration fee, and options. Not the list price before negotiation.
Check AutoTrader or Motorway for current market prices. For new cars use the manufacturer's configurator OTR price. Always use the price you'd actually pay, not the asking price.
DriveCalc uses UK market depreciation curves from Carmoola/Brego (40m+ car sales), AutoExpress, and Zutobi research to estimate how much value the car loses. Select the brand that matches your car.
If your exact brand isn't listed, pick the closest equivalent. Volkswagen is a reasonable proxy for most mid-tier European brands. Skoda/SEAT covers budget VW Group cars.
How old is the car when you buy it? Enter 0 for brand new, 1 for a one-year-old car, and so on. This sets your starting point on the depreciation curve. Older cars depreciate more slowly from that point — the steep early losses were taken by someone else.
Check the V5C registration document or the number plate. In the UK, March registrations = year start (23 plate = March 2023), September = mid-year (73 plate = September 2023).
If you'd rather look up the future value yourself, enter it here. This overrides the smart estimate entirely — make and age inputs are ignored.
Search AutoTrader or Motorway for the same make, model, and trim — but at the age the car will be when you sell it and with the mileage it will have by then. Average 3–5 similar listings.
Average yearly cost for servicing, tyres, MOT, and unexpected repairs. This only applies to the buy scenario — leased cars are typically new and under warranty.
Budget £300–500/yr for a reliable 1–3 year old car. £600–900/yr for a 4–7 year old car. £1,000+ for older or German premium brands. Ask your dealer about a prepaid service plan.
Vehicle Excise Duty (VED). Varies by CO₂ emissions and registration date. EVs now pay standard rate VED.
Look up the exact figure at gov.uk/check-vehicle-tax using the registration plate. Don't guess — rates changed significantly in April 2025.
Fuel (both scenarios, independent)
Petrol and diesel use litres and MPG. Electric uses pence per kWh and miles per kWh. The buy and lease scenarios have completely independent fuel inputs — you might be comparing a petrol used car purchase against a new EV lease, for example.
Current pump price per litre for your fuel type.
Check petrolprices.com for live prices near you. UK average petrol is around £1.45–1.55/litre. Use an average you're comfortable with, not a one-day snapshot.
Cost per kilowatt hour. Home charging is much cheaper than public rapid charging — use whichever reflects how you'd actually charge.
Check your energy bill for your home unit rate. Off-peak overnight tariffs (e.g. Octopus Go) can be as low as £0.07/kWh. Public rapid chargers average £0.55–0.85/kWh. Use a blended average if you do both.
Miles per gallon. Use a real-world figure — manufacturer WLTP numbers are typically 15–25% optimistic.
Fuelly.com has crowd-sourced real-world MPG by exact model and year. Or calculate it yourself: fill up, drive a known distance, fill up again, divide miles by litres used × 4.546.
How far the car travels per kilowatt hour consumed in real-world conditions.
Spritmonitor.de and EV Database have real-world efficiency data by model. A reasonable average for most EVs is 3–4 mi/kWh in mixed driving. Cold weather reduces this by 15–25%.
Lease scenario
The upfront payment at the start of the lease, often expressed as a multiple of the monthly payment. This amount is deducted from your purchase price when calculating how much you invest in the ISA.
Your lease quote will show this clearly. A typical initial rental is 1, 3, or 6 months upfront. Higher deposits reduce monthly payments but reduce your investable capital too.
Your fixed monthly payment for the duration of the lease, covering the car's depreciation over the contract plus the finance company's margin and profit.
Make sure you're using a figure that includes VAT. Personal Contract Hire (PCH) quotes sometimes show ex-VAT prices — add 20% if so. Check LeaseLoco.com to compare live deals.
The mileage allowance in your lease contract. Driving more than this results in a per-mile penalty charged at contract end.
Found in your lease quote. Don't underestimate your mileage — excess charges add up fast. It's usually cheaper to negotiate more miles upfront than pay excess at the end.
The per-mile penalty for going over your contract allowance. Charged on total excess miles across the whole contract, not per year.
Typically 5–15p per mile. Check your contract carefully — this is where many lessees get caught out at handback.
Many lease agreements bundle road tax into the monthly payment. Toggle on if your quote includes it; toggle off if you pay it separately.
The annual return you expect to earn on the money you would have spent buying the car, invested instead in a Stocks and Shares ISA. Defaults to 8%, a commonly cited long-run average for a diversified global equity portfolio.
If investing in cash savings, use your actual savings rate (likely 4–5%). If unsure, leave at 8% as a benchmark. This has a significant impact on the results — try different rates to see the sensitivity.
Insurance excluded from both
Insurance varies enormously by driver age, history, postcode, and car. Including a fixed figure would be misleading. Since it's broadly comparable either way, it's excluded from both sides.
Fuel price is held constant
The price you enter is used for the full period. Prices fluctuate in reality. Use a figure you're comfortable with as an average — not today's pump price if it's unusually high or low.
Maintenance is zero for lease
Leased cars are almost always new and under manufacturer warranty for the duration of a typical 2–3 year contract. Maintenance cost is therefore set to zero in the lease scenario.
ISA growth compounds annually
Investment growth uses annual compound interest: principal × (1 + rate)^years. No platform fees are assumed. A real ISA may have fees of 0.1–0.5% which would reduce growth slightly.
Depreciation assumes average condition
The smart depreciation curves assume ~10,000 miles per year and average condition with full service history. Higher mileage, poor condition, or a missing service history will accelerate depreciation.
All costs are in today's pounds
No inflation adjustment is applied. The model compares nominal cash flows. This is consistent and appropriate for a planning tool — just be aware that future pounds buy slightly less than today's.
Buy scenario ends with a sale
The model assumes you sell the car at the end of the period and recover the residual value. If you plan to keep the car long-term, the real depreciation cost is spread further and becomes cheaper per year.
Excess mileage is cumulative
Total excess = (your annual mileage × years) minus (lease included miles × years). The charge applies to cumulative excess across the whole contract, not on a year-by-year basis.
🚨 This only applies if you had the cash to buy in the first place
You have the cash — model applies
You have £25,000 in savings. You could buy outright or keep it invested and lease instead. The ISA growth offsets your lease costs. This is a genuine opportunity cost comparison and DriveCalc models it correctly.
You don't have the cash — model doesn't apply
You don't have £25,000. You'd need a loan, PCP, or HP to buy. There's nothing to invest — so the ISA field is meaningless. The comparison is lease vs. financed purchase, which is a different calculation entirely.
💡 What to do if you don't have the cash
📌 The bottom line
Your results are only as good as what you put in. Here's exactly where to find each number.
Current fuel prices
For EVs, use your home overnight rate unless you charge mostly on public rapid chargers. The difference between home and public charging rates is enormous — it changes the economics significantly.
Car purchase price
For used cars, average 3–5 similar listings to get a realistic market price. One listing could be an outlier. For new cars, remember to add any options or delivery charges to the base price.
Future residual value (manual mode)
Add your ownership period to the car's current age, search for that age and your expected total mileage. Example: buying a 2yr old car, owning for 3 years — search for 5yr old same model at your expected mileage.
Real-world fuel efficiency
Never use manufacturer WLTP figures — they are tested under ideal conditions and are typically 15–25% better than real-world for petrol/diesel, 10–20% for EVs. Real owner data from Fuelly is far more accurate.
Lease deal details
Always check whether the monthly figure shown includes VAT. Personal Contract Hire quotes from some brokers show ex-VAT prices — add 20% to get the real figure you'll pay.
Road tax (VED)
Road tax changed significantly in April 2025. EVs now pay standard rate VED for the first time. Always check the gov.uk tool rather than relying on old quotes or word of mouth.
Ready to run the numbers?
Head back to the calculator with your inputs prepared.
DriveCalc is a free planning tool. It is not regulated financial advice. Depreciation estimates are based on published UK market research and are indicative only. Always verify figures with current market data before making financial decisions.