Short answer. Twenty calendar days from service. Under Rule 11 of the Rules of Court, a counterclaim or cross-claim must be answered within twenty calendar days from the date it is served on you — a shorter period than the thirty calendar days allowed for answering an original complaint.
What the law says
A counterclaim or cross-claim must be answered within twenty calendar days from service.
Rule 11, Section 4 — Answer to counterclaim or cross. Read the full provision →
What the rule says
Rule 11, Section 4 is a single sentence: A counterclaim or cross-claim must be answered within twenty calendar days from service. The period is counted in calendar days, so weekends and holidays inside the period are included in the count; only a last day that falls on a Saturday, Sunday, or legal holiday moves the deadline to the next working day. The trigger is service of the counterclaim or cross-claim on you — usually as part of the answer that contains it — not any order or directive of the court.
Counterclaim and cross-claim, briefly
A counterclaim is a claim a defending party asserts back against an opposing party — most commonly the defendant suing the plaintiff within the same case. A cross-claim is a claim asserted against a co-party, such as one defendant claiming against another over the same transaction. In either situation, the person on the receiving end becomes, for that claim, a defendant, and the twenty-day period is the time to respond with an answer raising admissions, denials, and defences — just as with an original complaint, only faster.
Half the lead time you had for the complaint
Note the compression: an original complaint gives the defendant thirty calendar days from service of summons to answer, but a counterclaim or cross-claim gives only twenty from service. The Rules assume that by this point you are already in the case, already have counsel, and already know the dispute, so less lead time is needed. The practical consequence is that a plaintiff served with an answer should immediately check whether it pleads a counterclaim needing a response, because the twenty days are already running while the filing is still being digested.
The risk of silence
Claims pleaded against you and left unanswered can be taken against you: a party who fails to answer within the period may, on motion, be declared in default on those claims, with the court receiving evidence without their participation. Whether an answer is strictly necessary can depend on the nature of the particular counterclaim, but that is an assessment for a lawyer to make deliberately — not a position to back into by inaction. The safe course is simple: calendar twenty days from receipt, and either answer or get advice well within them.