Irish Calculators
Loans & mortgages

Car Purchase Budget and Trade-In Equity Calculator

Find the monthly payment available after your spending and savings buffer, then convert it to a purchase budget. Enter a trade-in value and debt or a known net equity; no vehicle price or credit approval is inferred.

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Your numbers

%
Monthly interest is the annual nominal rate divided by 12. This is not a fee-inclusive APR.
Your figures stay on this device.

How the calculation works

The purchase budget is built from money left each month after existing commitments, a savings buffer and vehicle running costs. That affordable payment is converted into a loan amount, then combined with cash and net trade-in equity.

Payment capacity = income − existing spending − savings buffer − running costs. Purchase budget = PV of non-negative payment capacity + deposit + net trade-in equity.

  1. Find the monthly margin

    Subtract spending, the safety buffer and running costs from income. A negative result stays visible as a shortfall, although it contributes no borrowing capacity.

  2. Convert payments into principal

    The loan amount is the present value of that non-negative monthly margin at the entered nominal rate and term. At zero interest it is simply payment capacity multiplied by months.

  3. Add available purchase funds

    Add the deposit and net trade-in equity to supported borrowing. The displayed purchase budget cannot fall below zero and is stated before transaction costs.

Worked example: Monthly budget converted to principal

Sample inputs demonstrate the method. They are not a forecast or product offer.

The example leaves €500 from €3,000 income after €2,000 spending, €300 savings and €200 running costs. Ten interest-free payments support €5,000 of borrowing. Adding €1,000 cash and €500 net trade-in equity produces a €6,500 purchase budget.

Monthly take-home income
3000
Monthly spending and existing debt payments
2000
Monthly savings and safety buffer
300
Monthly vehicle running costs
200
Available cash deposit
1000
Trade-in information
Net trade-in equity already known
Net trade-in equity after old debt
500
Annual nominal interest rate (%)
0
Remaining term (months)
10

Expected result

Monthly payment capacity
€500.00
Loan supported by non-negative capacity
€5,000.00
Purchase budget before transaction costs
€6,500.00
Worked example: Budget shortfall remains visible

Sample inputs demonstrate the method. They are not a forecast or product offer.

Monthly take-home income
1000
Monthly spending and existing debt payments
1000
Monthly savings and safety buffer
100
Monthly vehicle running costs
100
Available cash deposit
0
Trade-in information
Net trade-in equity already known
Net trade-in equity after old debt
0
Annual nominal interest rate (%)
0
Remaining term (months)
12

Expected result

Monthly payment capacity
-€200.00
Loan supported by non-negative capacity
€0.00
Purchase budget before transaction costs
€0.00

Understanding your result

The monthly margin is the starting constraint, not a recommendation to spend all spare income. Increasing the buffer lowers the amount available for repayments.

A longer term can support a higher purchase price for the same payment, but that does not establish affordability under lender rules or a favourable total borrowing cost.

Questions you might have

Why use net trade-in equity?

An old car worth €8,000 with €6,000 still owed contributes only €2,000 to the next purchase.

Choosing the right inputs

Monthly take-home income
Use monthly take-home income, since the other budget entries represent money you actually have to spend. This tool does not calculate deductions from gross salary.
Monthly spending and existing debt payments
Include regular living costs and existing debt payments once. Keep the separately entered new-vehicle running costs out of this total.
Trade-in information
Choose either known net equity or vehicle value less settlement debt. Negative trade-in equity reduces the purchase budget rather than adding purchasing power.

Common mistakes to avoid

  • Do not add the old vehicle value without deducting the debt that must be settled.
  • Budget insurance, fuel, maintenance and vehicle tax from your own figures; the calculator supplies none of those prices.

Assumptions to check

  • Running costs must include your own insurance, tax, fuel and maintenance estimates. Existing debts must appear only once.

Sources and method

Read our calculation and testing approach.