Separate the price from the cash you need
The agreed price is only one part of the cash required to complete. Start with the price and subtract only finance that is realistically available, then add transaction costs and a reserve. Deposits are usually payments towards the price when the agreement says so, so avoid counting them twice. Put each amount against its due date: having enough money overall does not mean it will be available when a payment falls due.
Calculate taxes for the actual transaction
The tax route depends on the nature of the transfer and the territory. Identify whether the transaction involves VAT, transfer tax or another applicable indirect-tax regime, and examine any stamp-duty component. For taxes administered by the autonomous community, check its current rules and the conditions of any relief. Where the reference value is relevant, the tax base may differ from the agreed price. Keep the assumptions and official source beside each estimate.
Request separate written estimates
List notary and Registry costs, legal assistance, any agency fee you have agreed, technical inspection, translation and administrative work. If borrowing, obtain a clear breakdown of costs relating to the mortgage as distinct from the purchase. A lender's provision of funds is not necessarily the final bill. Ask which figures include tax, what work they cover and how unused money will be reconciled after invoices are available.
Allow for the property you will actually own
Include urgent repairs, furnishings, insurance, utility changes and any known community contribution. With a foreign-currency budget, test how a less favourable exchange rate would affect the funds available. An off-plan purchase may also require rent or storage if delivery moves. Keep a reserve outside your maximum offer rather than assuming every unknown will cost nothing. Update the budget whenever an inspection, contract or tax calculation changes the picture.
Sources & further reading
Agencia Tributaria · Compra de vivienda: IVA o ITP ↗BOE · Ley de contratos de crédito inmobiliario ↗BOE · Información al comprador de vivienda (RD 515/1989) ↗Editorial preview: professional legal review is pending. This guide provides general information and does not determine the legal position of a particular property.
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Start by organising its documents and the questions still to resolve.