When must I oppose a Supreme Court mandamus or prohibition petition?

Identify the petition as one seeking mandamus, prohibition or both under Rule 20.3.

Verify when it was placed on the Supreme Court docket rather than using petition service or lower-court judgment entry.

All persons served are respondents for this proceeding. A named respondent choosing not to respond may advise the Clerk and all other parties by letter.

Check actual Court directions and any allowed Rule 15 extension before relying on the default date.

1. Use the petition’s Supreme Court docketing date. Confirm that the petition seeks mandamus or prohibition, rather than treating every extraordinary writ alike.
2. Exclude the established trigger day.
3. Count 30 calendar days.
4. Apply Rule 30.1 final-day adjustment.
5. Complete the required filing by that date.

Supreme Court Rule 30.1 excludes the trigger day and includes every intermediate calendar day. For periods shorter than seven days it excludes intermediate closed days. Each fixed period reviewed here is at least seven days.

Rule 20.3(b) incorporates Rule 15 fully. Rule 15.3 permits an authorized extension of opposition time. The calculator does not treat an application or another party’s extension as a grant.

If the final day is Saturday, Sunday, a federal legal holiday listed in 5 U.S.C. 6103 or a Court-building closure ordered by the Court or Chief Justice, Rule 30.1 continues the period to the next day that is none of those. Check actual Court closure orders. The calculator does not infer additional closures.

Fictitious example

Fictitious Supreme Court docketing of a mandamus petition on August 24, 2026. The respondent intends to oppose and no different schedule has been ordered. Exclude the established trigger day, August 24, 2026. Counting 30 calendar days reaches September 23, 2026. The final day is an open weekday.

Fictitious facts and dates. No different schedule, additional Court closure or extension is assumed.

Habeas is separate

Under Rule 20.4(b), noncapital habeas is ex parte unless the Court requires the respondent to show cause. Ordered or capital-case responses comply fully with Rule 15. Read the actual direction rather than automatically using this mandamus calculator.

No-response letter

A named respondent who does not wish to respond may advise the Clerk and all other parties by letter. The letter is not an opposition brief.

Copies and Rule 15 requirements

Rule 20.3(b) specifies forty copies and full compliance with Rule 15. Check applicable Rule 39 pauper procedure, service and any Rule 15 corporate disclosure obligation.

Distribution and later briefing

Rules 20.5–6 address distribution after the specified response, expiration or waiver branch and actual directions for additional briefs if argument is ordered. The thirty-day calculator does not predict distribution or merits briefing.

• The calculator counts the encoded default period after an established trigger. It does not determine jurisdiction, party alignment or the effect of a particular order.
• Check the Court’s docket, actual directions and proof of the required act.

• Confirm that the petition seeks mandamus or prohibition under Rule 20.3.
• Record actual Supreme Court docketing and all parties served.
• Check actual opposition extensions or Court directions.
• Prepare the opposition with applicable Rule 15, copy and service requirements.
• If choosing not to respond as a named respondent, notify the Clerk and all other parties by letter.
• Keep habeas response orders and any later merits briefing separate.
• Rule 29.2 distinguishes timely paper receipt, qualifying USPS postmark, commercial-carrier delivery and proper electronic submission. Under the March 2026 rule, electronic timeliness requires the paper copies to be delivered or mailed by a specified method within three days. Rule 29.7 and the current guidelines impose additional electronic-submission requirements for represented filers and identify exceptions. Filing with the Court does not itself transmit the document to other parties.
• Check represented-filer electronic requirements and paper-copy requirements. The March 2026 guidelines exempt specified sealed and privacy-sensitive filings from electronic submission.
• Preserve both filing and separate service evidence.