Binding period

In legal terms a proposal is an offer to conclude a contract, and whoever makes it is bound by it. Section 145 of the German Civil Code states this as a principle with a single exception: you are bound unless you have expressly excluded being bound. Name no period and section 147(2) applies, under which an offer made to an absent party can be accepted up to the point at which the offeror may expect the answer under ordinary circumstances. That is interpretation, not a number. Section 148 ends it: where a period has been set, acceptance can only take place within it. Austria says the same in section 862 of its Civil Code, there with the explicit addition that the offer cannot be withdrawn before the acceptance period expires.

For private proposals no statute prescribes a length. Where a figure was needed, it turned out short: under German construction procurement rules a binding period longer than 30 calendar days should only be set in justified cases, and its end must be stated as a calendar date. In Austria the acceptance period is one month where the tender names none, and may not exceed five months. Both sets of rules govern public contracting authorities rather than your proposal, but they work as a benchmark. The transferable rule is the form: a calendar date can be checked, a phrase such as valid for 30 days cannot, because it stays unclear when the counting started.

The binding period has two neighbours worth separating from it. A proposal marked as subject to change or non-binding is, under section 145, no longer a binding offer at all: the contract then only comes about with your confirmation. And a cost estimate is an estimate of cost, not an offer at a particular price. An expired period is no loss either: under section 150(1), late acceptance counts as a new offer. Someone getting back to you weeks later is therefore making you an offer, and you may recalculate without straining the relationship.