ABA Authorization Tracking: Units, Burn Rate, and How to Never Deliver Past the Cap

What a prior authorization is in ABA

A prior authorization is a payer's advance approval of medically necessary services before they are delivered. In ABA, the approval is specific: a set number of units for each CPT code (for example 97153, 97155, 97156), valid only between a start date and an end date. TRICARE's Autism Care Demonstration, for example, issues ABA treatment authorizations in six-month increments, with reauthorization required every six months. State Medicaid programs use the same structure — approved units per code within a date range; Nevada Medicaid requires prior authorization for adaptive behavior treatment codes, while initial behavior identification assessments (97151) do not require it and are limited to one per 180 days unless prior authorized.

An authorization is a ceiling, not a guarantee. The Texas Medicaid provider manual states plainly that "prior authorization is not a guarantee of payment" — reimbursement can still fail if the client loses eligibility on the date of service or the claim is incomplete. Nevada's ABA billing guide carries the same warning: authorization does not guarantee payment, which remains contingent on eligibility, available benefits, and coordination of benefits. Tracking therefore has two jobs: never exceed the cap, and confirm that what was rendered actually got paid.

Unit math: converting hours to 15-minute units

Every CPT code for adaptive behavior services — 97151 through 97158, plus 0362T and 0373T — is defined in 15-minute units, per the code descriptors published by the ABA Coding Coalition. One hour of service is 4 units. A weekly prescription converts directly: 10 hours per week is 40 units, 20 hours is 80 units, 40 hours is 160 units.

Typical prescriptions map to two treatment models. The Council of Autism Service Providers (CASP) guidelines describe focused ABA at roughly 10–25 hours per week and comprehensive ABA at roughly 30–40 hours per week. Payers encode similar bands: Nevada Medicaid defines its focused delivery model at 15–25 hours per week and its comprehensive model at 25–40 hours per week, applied to the combined units of 97153, 97155, and 0373T, with a limit of 40 hours per recipient per week across the treatment codes. As a daily sanity check, the CMS National Correct Coding Initiative sets the Medically Unlikely Edit for 97153 at 32 units — 8 hours — per patient per date of service, for both Medicare and Medicaid.

Why delivering past the cap means unpaid care

Units delivered beyond the authorized amount, or outside the authorization's date range, are generally denied and cannot be recovered later. The Texas Medicaid manual states that retroactive authorizations are not issued unless the service's regular procedures specifically allow post-service authorization — an exception that in Texas mainly covers retroactive Medicaid eligibility (authorization may be requested within 95 days of the client's eligibility add date), not late submissions. Humana Military, the TRICARE East contractor, is equally explicit for the Autism Care Demonstration: it "does not accept retrospective referrals and will not backdate late submissions."

The financial asymmetry is what makes this the most expensive tracking failure in an ABA agency. The sessions were staffed, the technicians were paid, and the documentation was written — but the revenue is zero and stays zero, because there is no back-billing path once the cap is passed. A single client over-delivering by two hours per week represents 8 unbillable units weekly, and the loss compounds silently until someone reconciles the ledger. Authorization tracking exists to make that reconciliation continuous instead of retrospective.

Burn rate: authorized vs. reserved vs. consumed

Robust tracking maintains three balances per authorization, per CPT code. Authorized is the cap from the authorization letter. Reserved (or scheduled) is the unit value of every future booked session through the end date — the calendar's forward commitment. Consumed is the unit value of sessions already delivered; behind it sit two lagging states, billed and paid, which confirm the payer's ledger agrees with yours.

Burn rate is consumed units per week measured from actual delivery, not from the treatment plan. Plans say 20 hours per week; reality adds make-up sessions, school-break intensives, and cancellations, so the real number drifts. Two checks catch every overrun before it happens. The projection check divides remaining units by the actual weekly burn rate to get an exhaustion date, then compares it to the authorization end date. The commitment check adds consumed plus reserved and compares the sum to authorized — if tomorrow's calendar already books more units than remain, the overrun is scheduled before it is delivered. Track each code's line separately: leftover 97155 supervision units do not offset an overrun on 97153 direct treatment.

Both checks are arithmetic, so a single authorization can be run by hand. The free authorization pacing calculator takes one grant's authorized, delivered and scheduled units and returns the exhaustion date, the weekly pace that lands exactly on the end date, and — where the payer set a weekly cap — the units that cap will strand before the period closes. It needs no account and runs entirely in the browser.

Worked example: a 2,080-unit authorization that exhausts two and a half weeks early

Take a client authorized for 20 hours per week of 97153. That is 80 units per week, and a six-month authorization sized to the plan holds 2,080 units across 26 weeks (80 × 26). Delivered exactly to plan, the units run out on the authorization's last day.

Now let the schedule over-deliver modestly: make-up sessions and an added school-break block push actual delivery to 22 hours per week, or 88 units. At that pace the 2,080 units last 2,080 ÷ 88 ≈ 23.6 weeks — the authorization exhausts during week 24, roughly two and a half weeks before its end date. If the calendar keeps running at 88 units per week through week 26, the agency delivers about 208 unauthorized units, which is 52 hours of unpaid care for one client.

The burn-rate check catches this months ahead. At week 12 the ledger shows 1,056 units consumed against a planned 960 — a 10% overrun. Remaining units are 1,024; divided by the actual 88-unit weekly burn, exhaustion projects at week 23.6, flagged 11 weeks in advance. With that lead time the agency can trim the schedule back toward 80 units per week, or request more units while the authorization is still active — Nevada Medicaid, for instance, accepts unscheduled revision requests during an existing authorization period when a change in the recipient's condition warrants it.

Warning thresholds and reauthorization lead times

Reauthorization windows are payer-specific, and the differences are large enough that each authorization should carry its own submission deadline. Under TRICARE's Autism Care Demonstration, authorizations run six months; Humana Military accepts ongoing-treatment requests up to 60 days in advance and warns that submitting less than 30 days before the current authorization expires may result in non-reimbursement. Nevada Medicaid requires continued-service requests to be received by the last authorized date and recommends submitting 5 to 15 days prior. A commonly cited operating target across payers is submission at least 30 days before expiry, but the payer's own published window always governs.

The clinical lead time is longer than the submission window. Reauthorization packets require updated progress data and a revised treatment plan, and TRICARE additionally requires four standardized outcome measures on a recurring schedule (every six or 12 months, depending on the measure) — work the BCBA must start weeks before the submission deadline. In practice agencies layer alerts on both dimensions: percentage of units consumed (for example, review at 75% and escalate at 90%) and days until expiry without a submitted reauthorization. The specific percentages are operational convention rather than regulation; what matters is that the alert fires while corrective action is still possible.

Coverage gaps between authorization periods

A coverage gap opens when a new authorization starts later than the old one ends — usually because the reauthorization was submitted late, pended for missing documentation, or delayed in payer review. Sessions delivered inside the gap sit outside any authorization's date range, and payers that refuse to backdate will not cover them; Humana Military states it will not backdate late submissions. Nevada's technical-denial process illustrates how quickly a pend becomes a gap: incomplete prior authorization requests give the submitter five business days to supply missing information before denial.

Agencies handle gaps in three ways, and the choice should be explicit rather than accidental. First and best, prevent them: submit at the earliest point the payer's window allows, and treat an authorization expiring without a submitted reauthorization as an operational emergency, not a task. Second, if a gap is unavoidable, pause services and communicate the clinical rationale and restart date to the family. Third, some agencies knowingly continue care through a short gap at their own cost — a defensible clinical decision only when leadership makes it deliberately, with the write-off quantified in advance.

What to track for every authorization

A complete authorization record makes every downstream question answerable without calling the payer. The distinction between rendered and paid matters most at the edges: rendered units measure your exposure, while paid units confirm the payer's count matches yours — a divergence between the two is often the first visible symptom of an authorization mismatch on claims.