8-Minute Rule Calculator
Enter each timed CPT code and its minutes, pick a methodology, and see billable units per code — under the CMS 8-minute rule or the AMA Rule of Eights. Built for therapists: OT, COTA, PT, and PTA.
| Code | Minutes | Units |
|---|
Two codes tie on remaining minutes — the extra unit is shown on the first-entered code, but it may be assigned to either service.
Heads up: the CMS 8-minute rule and the AMA Rule of Eights give different results for this input.
This calculator is an informational tool, not billing or coding advice. Unit calculation methods vary by payer — verify against your payer’s policy before submitting.
Minutes-to-units chart
Under the CMS 8-minute rule, total timed minutes convert to units in 15-minute increments, starting at 8 minutes. The AMA Rule of Eights uses the same thresholds, applied to each code separately.
| Timed minutes | Billable units |
|---|---|
| 0 – 7 | 0 units |
| 8 – 22 | 1 unit |
| 23 – 37 | 2 units |
| 38 – 52 | 3 units |
| 53 – 67 | 4 units |
| 68 – 82 | 5 units |
| 83 – 97 | 6 units |
| 98 – 112 | 7 units |
| 113 – 127 | 8 units |
What the CMS 8-minute rule is
The 8-minute rule is how Medicare converts time-based therapy services into billable units. You add up all timed minutes for the visit — across every time-based code — and read the total off the chart above. At least 8 minutes of skilled, timed service must be furnished before any unit can be billed.
Total units are then allocated across the codes you billed: each code earns one unit per full 15 minutes, and any additional unit produced by the combined remainders goes to the service with the most remaining minutes. The rule is published in the CMS Medicare Claims Processing Manual, Chapter 5.
What the AMA Rule of Eights is
The AMA’s Rule of Eights — the Substantial Portion Methodology — uses the same minute thresholds but applies them to each code independently. A code with at least 8 minutes bills units from its own minutes alone; a code with fewer than 8 minutes bills zero, no matter how long the rest of the visit ran. Minutes are never pooled across codes.
When each rule applies
- Medicare Part B follows the CMS 8-minute rule, and most Medicaid programs and many payers align with it.
- Some commercial payers follow the AMA Rule of Eights instead.
- The two methods can disagree on the same visit — when they do, this calculator flags it. Your payer’s policy is the one that governs.
A worked example
Say a session has 23 minutes of therapeutic exercise (97110) and 7 minutes of neuromuscular reeducation (97112).
- CMS: 23 + 7 = 30 total timed minutes → 2 units (23–37 range). 97110 earns one unit for its full 15 minutes; the leftover unit goes to the service with the most remaining minutes — 97110’s 8 beats 97112’s 7. Result: 97110 × 2, 97112 × 0.
- AMA: each code stands alone. 97110’s 23 minutes are 2 units on the chart; 97112’s 7 minutes are below the 8-minute threshold and bill 0. Result: 97110 × 2, 97112 × 0 — the same in this case, though other inputs diverge.
Untimed, service-based codes (like unattended e-stim) sit outside both methods: one unit per session, and their minutes never join the timed pool.
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