🧾 How to calculate the real profit in a second-hand car sale (with REBU and well-explained margins)

In the world of buying and selling used vehicles, calculating your margins correctly is not just a good practice: it is a survival tool. Understanding the difference between the operating margin, the real margin, and the effect of taxes (like the REBU) allows you to make smarter decisions and avoid typical mistakes that distort profits.

🧩 Basic Margin Schema

1. ✅ Buying and Selling Margin (or Operating Margin)

This is the simplest calculation:

Margen Compraventa = Precio de venta – Precio de compra

🔹 It only reflects the difference between what you paid and what you charged for the car.
🔹 It does not include additional expenses or income.

2. 💡 Gross Margin

Here you take into account the associated income and expenses of the operation.

Margen Bruto = Margen Compraventa + Ingresos adicionales – Gastos asociados

✅ Includes:

• Income: financing commissions, warranty sales, logistics, insurance...

• Expenses: cleaning, refurbishing, management, marketing, transportation...

3. 🧾 Net Margin

This is your real profit, after deducting taxes.

Margen Neto = Margen Bruto – Impuestos (IVA incluido en REBU o IS)

🧮 Complete Example with REBU

• Purchase price: 8,000 €

• Sale price (customer): 10,000 €

• → Buying and Selling Margin: 2,000 €

Let's assume:

• Additional income (financing commission + warranty): 400 €

• Associated expenses (workshop + advertising): 700 €

• → Gross Margin: 2,000 + 400 – 700 = 1,700 €

Now we apply the REBU VAT:

❓ How is VAT calculated in REBU?

In the REBU regime, VAT is already included in the margin, it is not added as in a traditional invoice.

To know how much it is, you have to calculate the tax base and then the VAT included in that margin.

🔍 What is the taxable base?

The taxable base is the value without VAT on which the tax is calculated.

In the case of REBU:

Base imponible = Margen Bruto / 1,21
IVA incluido = Margen Bruto – Base imponible

📌 You divide by 1.21 because you are separating 100% of the value + 21% of VAT, meaning you are breaking down a price that is already included.

🧮 Application to the example

• Gross Margin: 1,700 €

• Taxable base = 1,700 / 1.21 = 1,404.96 €

• VAT included = 1,700 – 1,404.96 = 295.04 €

→ Real Net Margin = 1,404.96 €

🛑 Warnings (Common mistakes to avoid)

1. ❌ Calculate VAT as 21% of the margin

   • Incorrect example: 2,000 € × 0.21 = 420 €

   • ✅ CORRECT: divide by 1.21 because VAT is already included.

2. ❌ Confuse gross margin with real profit

   • If you do not deduct expenses or taxes, you are overestimating your profitability.

3. ❌ Forget to include extra income

   • Warranties, insurance, and financing can add up to 400-600 € per car.

4. ❌ Not keeping traceability per car

   • Without individual tracking, you won't really know which cars make you money or lose you money.

✅ Conclusions

• The buying and selling margin is just the starting point.

• The gross margin gives you a more realistic view, including everything that comes in and goes out.

• The net margin, especially with REBU, gives you the real profit after taxes.

• To calculate REBU correctly, remember:
  divide the margin by 1.21 to get the taxable base and know the included VAT.