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The 8-minute rule, calculated
Enter the timed minutes for each code and get the correct Medicare unit count, plus the code-by-code split, including the leftover unit that trips up most billers.
Enter face-to-face minutes for each timed (15-minute) code. Untimed codes like 97010 and G0283 are billed as one unit each and are not part of this math.
Total billable units 53 min
4 units
53 timed minutes bills 4 units. The leftover unit goes to the code with the most unbilled time.
The split, per code
Medicare 8-minute rule: total all timed minutes, take one unit per whole 15-minute block, and add one more unit only if the remaining minutes are 8 or more. When codes are mixed, the leftover unit is assigned to the code with the most unbilled time. This is the CMS method; some commercial payers use the AMA rule of eights instead, which counts each service separately and can yield a different total.
The chart, and the number everyone remembers wrong
Once you total your timed minutes, the unit count follows this table. There is nothing to interpret; it is a lookup.
| Total timed minutes | Billable units |
|---|---|
| 8 to 22 | 1 |
| 23 to 37 | 2 |
| 38 to 52 | 3 |
| 53 to 67 | 4 |
| 68 to 82 | 5 |
The classic mistake is 47 minutes. It feels like it should round up to four units, but three whole blocks is 45 minutes and the 2 leftover minutes are under 8, so it stays at three units. The calculator above never makes that error.
Why the leftover unit matters
When a session mixes codes, you cannot just round each code on its own. You total the minutes, find the total units, give each code its whole blocks, and then hand the one leftover unit to the code with the most unbilled time. That is how 30 minutes of therapeutic exercise, 15 of neuromuscular re-education, and 8 of manual therapy becomes four units split 2, 1, 1, with manual therapy earning a unit off just 8 minutes because it had the most time left unbilled. Bill each code in isolation and you would drop that unit and underbill the visit.