Short answer. Fifteen days in most cases. A motion for reconsideration must be filed within the period for taking an appeal, which is ordinarily fifteen days from notice of the judgment or final order. Filing on time interrupts the appeal period; filing late leaves the judgment to become final and executory.
What the law says
Within the same period, the aggrieved party may also move for reconsideration upon the grounds that the damages awarded are excessive, that the evidence is insufficient to justify the decision or final order, or that the decision or final order is contrary to law.
Rule 37, Section 1 — Grounds of and period for filing motion for new trial or reconsideration. Read the full provision →
Tied to the appeal period
Rule 37, Section 1 does not state its own number of days; it borrows the appeal clock. A motion for new trial must be filed Within the period for taking an appeal, and the section adds that Within the same period, the aggrieved party may also move for reconsideration. For most civil judgments the period for taking an appeal is fifteen days from notice of the judgment or final order, so the motion for reconsideration must be filed within those same fifteen days — counted from receipt of the decision, not from the date typed on it.
The grounds that qualify
Reconsideration is not a free-form second try. The motion must rest on the grounds the section names: that the damages awarded are excessive, that the evidence is insufficient to justify the decision or final order, or that the decision or final order is contrary to law. A motion that merely repeats earlier arguments without tying them to one of these grounds risks being treated as pro forma — and a pro forma motion does not stop the appeal clock. The stronger motions identify the specific findings said to be unsupported and the specific legal rules said to be violated.
Reconsideration or new trial?
The same section offers a different remedy for a different kind of problem. New trial lies for Fraud, accident, mistake or excusable negligence that ordinary prudence could not have guarded against, or for Newly discovered evidence that reasonable diligence could not have produced at trial. Reconsideration, by contrast, attacks the decision on the record as it stands. If your real complaint is that something outside the record went wrong — you never got to present your evidence, or decisive proof surfaced only now — the motion to consider is new trial, filed within the very same period.
The period is unforgiving
Two consequences follow from tying the motion to the appeal period. First, the Rules do not allow a motion for extension of time to file a motion for new trial or reconsideration; the period you have is the period you get. Second, if no timely motion or appeal is filed, the judgment becomes final and executory by operation of law, and the trial court loses the power to change it. Count the fifteen days from the date of receipt shown on the registry return card or electronic notice, and file within them — the calendar, not the merits, decides this stage.