PetrolCalculator

Finance calculator

Car Finance Deposit Calculator

Estimate the deposit needed to reach a chosen monthly payment under a standard amortising finance model.

Use this calculator

Enter a car price, payment budget, APR and term to estimate the deposit needed.

What your result means

This page starts with a known car price, monthly-payment budget, APR and term. It works backwards to estimate the principal that the chosen payment could support, then calculates the deposit needed to bridge the gap to the car price.

If the payment can support the full entered price, the required deposit is shown as £0. That does not mean a lender will offer zero-deposit finance; it only describes this standard amortising calculation.

Worked example

Illustrative inputs only: £20,000 car price, £400 target payment, 6% APR and a 48-month term.

Estimated amount financed
£17,032.13
Estimated required deposit
£2,967.87
Deposit percentage
14.8%
Estimated total repayments
£19,200.00
Estimated interest
£2,167.87

The calculator reverses the standard payment model using the same tested finance-deposit helper.

Formula

Payment×1−(1+APR1200)−MonthsAPR1200\text{Payment}\times\frac{1-\left(1+\frac{\text{APR}}{1200}\right)^{-\text{Months}}}{\frac{\text{APR}}{1200}}
max⁡(Car price−Financeable principal,0)\max\left(\text{Car price}-\text{Financeable principal},0\right)
Monthly payment×Months\text{Monthly payment}\times\text{Months}

Target-payment sensitivity using illustrative price, APR and term

Target monthly paymentEstimated depositDeposit percentageEstimated amount financed
£300.00£7,225.9036.1%£12,774.10
£350.00£5,096.8925.5%£14,903.11
£400.00£2,967.8714.8%£17,032.13
£450.00£838.864.2%£19,161.14
£500.00£0.000%£20,000.00

Working backwards from a monthly budget

The known values are the car price, monthly-payment budget, APR and term. The helper solves for the amount of principal that those monthly payments can amortise, then subtracts that amount from the car price.

At 0% APR, the financeable principal is simply monthly payment multiplied by the term. At a positive APR, part of each payment goes to interest, so the financeable principal is lower for the same payment and term.

What this deposit estimate is not

This is a standard amortising finance model only. It does not model a PCP balloon payment, lender affordability assessment, credit eligibility, manufacturer contribution, product fee, optional extras or a lending offer.

A lender may require a different deposit or may not lend the modelled amount. Use actual quotes and agreement documents when making a purchase decision.

Practical guidance

Try several payment budgets while keeping the price, APR and term realistic. A higher payment or longer term can reduce the calculated deposit, but a longer term can also increase the total interest paid.

Treat the result as a planning estimate, not a borrowing decision. Check the full cost, product fees, affordability and available finance offers before committing to a car purchase.

Assumptions and limitations

  • The model uses a fixed APR and equal monthly payments across a whole-number term.
  • The financeable amount is capped at the entered car price, so the result never implies a negative deposit or money paid back to you.
  • Fees, lender criteria, credit checks, optional extras, trade-in value and lender contributions are excluded.
  • This is not PCP balloon-payment modelling, an affordability assessment, a credit decision or a lending offer.

Helpful questions

How is the required deposit calculated?

The model calculates the principal that the target payment can support at the APR and term entered, then subtracts it from the car price.

Why does a higher monthly payment reduce the deposit?

A higher payment can amortise more principal over the same term, so less of the car price needs to be covered upfront.

What if the result is £0 deposit?

The entered payment can support the full car price in this calculation. It does not mean a lender will actually offer zero-deposit finance.

Does this work at 0% APR?

Yes. At 0% APR, the model uses monthly payment multiplied by the number of months as the financeable principal.

Is this a PCP calculator?

No. PCP can include a balloon payment. Use the PCP Car Finance Calculator for a PCP payment structure.

Can I compare the deposit with a normal loan payment?

Yes. The Car Loan Calculator estimates standard monthly payments from an entered loan amount and term.

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