Insurance · Updated 2026-09-08 · 5 min read

What does '1 per 36 months' mean?

It means not yet. A rolling window counts backwards from your last date of service — and plans differ on whether it is counted to the exact day or to the month.

Not yet. "1 per 36 months" is a rolling window measured backwards from the date of service, so at 35 months the previous service is still inside the window and the claim is refused. Only a calendar-year or benefit-year limit resets on a date; a rolling limit resets on the anniversary of the patient's own last visit. Two things then decide the exact day. First, the granularity: some plans count to the exact day, some to the calendar month, and some in elapsed days. Second, the anchor: the window runs from the last covered date of service, or from the placement date on a restoration, and one plan's wording can differ from another's on the same code. In one 30-day sample of whole-claim refusals in September 2026, frequency limits were the reason that could have been read off the plan beforehand on 38 of 39 claims.

What we measured

A 30-day sample of whole-claim refusals to 18 August 2026, split by the reason the payer stated; the credentialing rows carried $103,258. A frequency refusal is nearly always a limit that was already published on the plan before the appointment — which is exactly why the arithmetic is worth getting right.

What the carriers' own policies say

The granularity differs by procedure family inside a single plan: "The 24-month time limitation for periodontal services (e.g., osseous surgery, etc.) is based on the exact date of service (day and month) … The 36-month time limitation for a panoramic or complete series of x-rays or a denture reline/rebase is calculated to the month in which the service was performed" (TRICARE Dental Program Handbook Supplement – Benefits Booklet, January 2025).

The sharpest illustration of what "six months" can mean is a state manual: "This examination is limited to once every six months (per calendar month) for eligible Medicaid recipients. A full six month period between oral exams is not required. For example, if a recipient received an oral exam on January 15, 2002, he or she is eligible for another exam any time in July 2002 (the sixth month)" (Alabama Medicaid Provider Manual Chapter 13 – Dentist, January 2026).

Now put a second state programme beside it, counting elapsed days for the same benefit: the cleaning entry reads "1 per 180 days" while the prose on the same page says "Normal cleanings are once every 6 months" (Vermont Medicaid Dental Supplement, May 2026). The January-15 patient who is eligible "any time in July" in Alabama is refused on day 179 in Vermont.

The anchor, stated plainly by the one carrier that publishes a genuinely carrier-wide schedule, Physicians Mutual: "The frequency is measured forward from the last covered date of service for the procedure" (Over 400 Covered Dental Procedures, Physicians Mutual, retrieved 2026). And an insurer's plan handbook stating both bases in two sentences: "All annual or per year benefits or cost sharing accrue based on a calendar year (January 1 through December 31). Frequency limitations are calculated from the previous date of service or initial placement, unless otherwise specified" (Delta Dental PPO 1000 Oregon Group Dental Plan Handbook 2026 Sample, 2026).

And a rolling window does not reset when the plan year does: "There must be a six month separation between services, even when the separation of services duration enters a new plan year" (The MetLife Federal Dental Plan 2025 FEDVIP Brochure, OPM, 2025).

Why it depends on the plan

The wording form carries the answer, and a handful of forms do most of the work. "1 per 36 rolling months" and "1 per 36 mos" say it outright. "Once Per 5 Consecutive Years" and "Four Per 12 Consecutive Months" mean the same thing: consecutive is rolling from the last date of service, so five consecutive years is sixty rolling months rather than five anniversaries. "1 in a 6 month period" and "2 in a 12 month period" read like an annual count and are rolling windows. "1 Every 1 Accum Year(s)" is an accumulated — rolling — year. "2 per calendar year" is the one form that genuinely resets on a date.

Some carriers state the precision on the face of the limit. Two of them print "1 per 24 months to the exact day", and one prints "covered once each quadrant in any 36 months to the exact day" — under that rule, 23 months and 29 days is too soon.

Two more forms are not time windows at all and are easy to misread as one. "1 per Day" or "5 per Day" caps how many can be billed on a single date of service. And a limit printed as "0 in 12 months" is a missing count rather than an exclusion — the same benefit is rendered elsewhere as one per twelve months.

What to do

• Ask for the last date of service the carrier holds for that code, not the patient's recollection. The window runs from the carrier's date.
• Ask whether the window is counted to the day or to the month. Where a plan counts to the month, the first day of the Nth month qualifies; where it counts to the day or in days, it does not.
• Where the carrier publishes a next eligible date per benefit, take it and diary it. At least one carrier states the date outright rather than leaving the office to compute it.
• Read "consecutive", "rolling" and "in any N month period" as the same instruction: count backwards from the last visit.
• On a restoration, check whether the anchor is the last date of service or the original placement date. Those are different dates and the plan says which.
• If the patient is within a month or two of the window, say so and give the date. A visit moved by three weeks is cheaper than an appeal.

Numbers last refreshed September 2026.

All articles · Kaylie