Building Society Savings Contract
Also known as: Bausparvertrag, Contractual savings for housing, Épargne-logement
Save at a below-market rate now to earn the right to borrow at a below-market rate later. A forward-starting mortgage option, sold as a savings account.
- Asset class
- Money markets (contractual savings)
- Instrument type
- Savings phase plus a loan option
- Traded
- Not traded; assignable in some jurisdictions
- Typical users
- Households in Germany, Austria, France, Czechia and others
1 · SnapshotThe one idea to remember
2 · BeginnerWhat is it, really?
A building society savings contract runs in two phases. First you save — usually for six to eight years, at an interest rate deliberately below what an ordinary deposit pays. Once you reach an agreed share of the contract sum, you earn the right to a loan at a rate fixed when you signed, years earlier.
Judged as a savings account it looks poor, and that judgement misses the product entirely:
- The interest you gave up is the premium. You paid it, in instalments, over several years.
- What you bought is an option — the right, never the obligation, to borrow at a rate locked in long ago.
- Options have value when rates move. If mortgage rates are far higher when you draw the loan, the option pays. If they are lower, you let it lapse and take the market rate instead.
Millions of households hold one of these without ever describing it as a derivative. It is one, and it is a long-dated interest-rate option written by a specialist institution.
3 · IntermediateHow it works in practice
The two phases
| Savings phase | Loan phase | |
|---|---|---|
| Duration | Typically 6–8 years | Up to ~10–12 years |
| Rate | Below market, fixed | Below market if rates rose, fixed |
| Your position | Paying the premium | Exercising the option |
| Requirement | Reach an agreed share of the contract sum | Use for qualifying housing purposes |
The closed system, and why it exists
These institutions historically operated as a collective: savers' deposits fund other members' loans, largely insulated from wholesale markets. That structure gives the model its resilience and its rigidity — allocation depends on the pool having enough savers, which is why waiting times lengthen precisely when many members want to draw loans at once.
The fees, which are where the value usually goes
- An acquisition fee of roughly 1–1.6% of the contract sum, charged up front on money not yet saved. On a €50,000 contract that is €500–800 before a cent of interest accrues.
- Annual account fees during both phases.
- State subsidies in several countries offset part of this for lower-income savers, and they are genuinely material where available — but they are policy, not product.
4 · AdvancedPricing & valuation
Valuing it as what it is
- The loan right is economically a long-dated payer swaption: the right to pay a fixed rate on an annuity. Price it with the same machinery as the swaption page describes, using the loan's annuity factor from the swap calculator.
- The option is deeply out of the money in a low-rate world and valuable in a rising-rate one. Contracts signed in the 2010s at loan rates near 2% became genuinely valuable after 2022 — and the same contracts had been widely criticised as poor value for the preceding decade. Both assessments were correct at the time.
- The institution is short that option to millions of households simultaneously, which is a real and correlated exposure. It is hedged partly by the closed system's structure and partly by the fact that many savers never exercise.
The behaviour that decides the outcome
- A large share of contracts are never used for a loan at all. Those savers paid a multi-year option premium and let the option expire — the single most common way to lose money on this product, and it requires no market move.
- Institutions have at times terminated old, high-rate savings contracts held by savers who had no intention of borrowing. Courts in several jurisdictions have permitted this after a defined period, which is a reminder that the contract's optionality runs in both directions.
- The qualifying-use requirement is binding. The loan must generally fund housing, and the definition is specific. A saver whose plans change may find the option unusable rather than merely unattractive.
How to assess one
Three questions settle it, and none of them is the advertised savings rate:
- What is the total premium? Foregone interest over the savings phase plus all fees, in currency.
- How far must mortgage rates rise for the loan rate to recover that premium over the loan's life?
- How likely are you to actually take the loan, for a qualifying purpose, in that window?
If the answer to the third is "probably not", the first two are irrelevant — an option you will not exercise is worth nothing regardless of where rates go.
The formulas above are standard textbook formulations, simplified for teaching. They explain the mechanism — they are not a valuation tool, and they will not reproduce a dealer’s price.