Mandatory date or binding date?

Mandatory or binding – which is the better word? Here is the context: I'm dealing with a contract that forces me to complete one task by a specific date. Is this a mandatory date, or a binding date? Which word is better?

Could you suggest an alternative word if one is more appropriate?

I think binding (which, according to NOAD, means impose a legal or contractual obligation on) is the more fitting word here. Mandatory simply means something is mandated (such as a mandatory helmet law for motorcyclists); binding implies that something (such as a date) has been agreed to by both parties.

As for alternative suggestions, you might consider contractual deadline, but I'm no expert in contract law. A lawyer could probably give you a better answer.

The date is mandatory;¹ the contract is binding.²

In law, to bind means to create a legal duty by your promise. When you make a contract, or swear an oath, you bind yourself. The Latin derived term obligation has the same meaning: ob- + ligare, “to bind (someone) to”.

Mandatory means “commanded” (and therefore something you have no choice about). In this case, the contract commands you to complete the task on time.