1. Family loan agreement (Spain: Modelo 600)
You finish university and the first flat, the first car or the first business opportunity shows up. Almost always with family money in the middle. What nobody tells you: if the transfer is over a few thousand euros and there is no written agreement, the Spanish tax agency treats it as a gift, not a loan. That means thousands of euros in Inheritance and Gift Tax depending on the region.
The fix costs zero euros: a loan agreement between private parties + Modelo 600 filed within 30 days (it is exempt of stamp duty if there is no interest). The contract states when the money is paid back, in which instalments, and at what rate (it can be 0% if you cite article 1755 of the Civil Code). With that, your parents can help you with a down payment without either of you losing sleep for the next four years of tax statute of limitations.
2. Cohabitation agreement (if you live with an unmarried partner)
Most twenty-somethings sharing a flat with a partner are neither married nor registered as a civil partnership. For the law, that makes them two strangers splitting bills. If the relationship ends badly there is no automatic legal framework to decide who keeps what — especially if one party put more money into the deposit, the furniture, the down payment or even the pet.
A cohabitation agreement puts in writing: who pays what, how the deposit is split if you move out, what happens to jointly-bought goods, and how an exit works if one of you leaves first. Not romantic, but the day someone forgets to pay their half of the internet bill by mistake, both parties will be grateful.
3. Free vehicle loan (lending a car to a friend or relative)
You lend your car to your sister while she is on Erasmus, or to your best friend during the summer. Standard. What almost nobody knows: if that person gets a speeding ticket or an accident without witnesses, the legal driver is still the vehicle owner (you) until you prove otherwise (art. 9 bis of Spanish Royal Decree 6/2015).
A free-use agreement (comodato under art. 1740 of the Civil Code) sets out: state of the car at handover, term, who pays fines, who pays the MOT and maintenance, and what happens if there is an accident. A single A4 sheet that avoids paperwork chaos for the months the loan lasts.
4. Parental authorisation for a minors travel
Maybe not for you anymore — but if your younger sibling or nephew is travelling with only one parent, with grandparents, or in a school group abroad, border police can demand the authorisation signed by the other parent. Without it: missed flight, paid hotel, airport tears.
The document (apostilled or not depending on the country) cites the 1980 Hague Convention on international child abduction and is either signed before a notary or printed out. It only costs time and foresight.
5. Verbal or written? Spoiler: verbal is valid but unprovable
The Spanish Civil Code (art. 1278) accepts verbal contracts for almost anything: sale, loan, services. The problem is not validity — it is proof. The day your cousin denies he promised to pay back the 800€ in six months, or a client claims the price was 400 not 800, without paper you have nothing. Just your word against theirs.
Simple rule of thumb: if the amount would hurt to lose, write it down. Even a WhatsApp saying "I confirm I am lending you 800€ until 31 December" plus the other partys reply works. WhatsApp threads count as electronic documentary evidence if properly archived (art. 326 of the Spanish Civil Procedure Act and consolidated case law).
6. Debt acknowledgement (when it is already too late)
Tip number five reached you late and your cousin now owes you 1,500€ from two years ago with no paper trail. Not all is lost. A debt acknowledgement is a signed document where the other party confesses the debt, sets a payment plan and, crucially, restarts the statute of limitations (art. 1973 of the Civil Code). Even if the original debt was old, from the date of the new acknowledgement you have a fresh 5-year window to claim.
It also helps formalise informal family debts before they grow. Bonus: with acknowledgement plus bank transfer record, the small-claims procedure in Spanish courts is fast and cheap (no lawyer required up to 2,000€).
7. Basic NDA (non-disclosure agreement)
At 25 you may have to show your app idea to a freelance developer for a prototype. Or share your business plan with an experienced friend before fundraising. Without a basic NDA that person can replicate it, tell someone or use it in their next job. Not necessarily out of bad faith: simply because nothing prevents it.
A one-page NDA defines what counts as confidential, how long the duty lasts (typically 2-5 years), what happens on breach (penalty clause) and the applicable jurisdiction. Whoever refuses to sign it is already telling you a lot about whom you are dealing with.
Bonus: when you start a project with friends
Three friends launch an app, a YouTube channel or a small business."We will sort it out when we make money." Five months later one leaves, another stops showing up and things start to take off. How is it split? Without a founders agreement (vesting, cliff, drag-along), everything turns into argument. Better to start with a simple piece of paper, even before the company legally exists.
Why having these before 30 changes your adult life
Contracts are not for old people or corporations. They are the adult way of saying "this is what the two of us agreed at this moment". The difference between a generation that signs everything by trust and one that writes everything down is not distrust: it is clarity. When everything is on paper, nobody argues at the end of the year.
The seven contracts above cover the most common situations before 30: money between family, life with an unmarried partner, helping friends, first business ideas. Twenty minutes of preparation today saves you years of lawsuits or broken relationships tomorrow.
The questions we get every time we explain this
"Does this work legally without a notary?" Yes. The legal validity of a private contract between individuals does not require notarisation in the vast majority of cases. A notary provides a certain date and permanent archive, but is not needed for the contract to be valid (art. 1278 of the Civil Code). Only mortgages, gifts of real estate, marriage capitulations and inheritances require notarial deed.
"Do I need to pay to sign?" No. Most templates are free. Runican free plan lets you create up to 3 active contracts and fill up to 3 base templates with no credit card. You only pay if you need custom templates or bulk generation.
"How do I share the draft with the other party?" The most convenient flow is the third-party form: you create the contract as the maker, generate a unique link, the other party fills their fields without needing an account, sees a preview with their data highlighted, signs and everything is recorded with a cryptographic verification hash. Each party keeps the signed PDF.
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