AR in medical billing: aging tells you how old, not how urgent

Accounts receivable (AR) is the money a practice has earned and not yet collected. Every billing team watches it the same way, in 30-day aging buckets. The buckets make a good report and a poor worklist, because a claim's age says nothing about how long you have left to get it paid.

In medical billing, AR is every dollar billed for care already given that has not been paid yet. It is owed from two directions. Insurance AR is what payers still owe on claims that have been submitted. Patient AR is what is left for the patient once the payer has adjudicated the claim: the deductible, coinsurance and copay, which come back on the remit as PR-1, PR-2 and PR-3.

A claim enters AR when it is billed. HFMA's MAP Keys, which HFMA publishes as the industry-standard revenue cycle metrics, count only billed accounts in billed A/R. Care that has been given but not yet billed is tracked separately, which is worth knowing when two reports disagree on the total.

The usual example goes like this: a provider bills a payer $500, the payer has not paid yet, so $500 sits in AR. That is true on the day it is billed. Then the remit comes back and splits it. Here is one way that plays out on a plan with a $320 contracted rate, 20% coinsurance and the deductible already met.

Only $320 of the $500 was ever collectible. The other $180 is a contractual adjustment, which the payer reports as CO-45: the charge exceeds the fee schedule or contracted amount. It is not a denial and there is nothing to appeal. You post it and it comes off AR. The $64 does not disappear either. It moves from insurance AR to patient AR, and someone has to bill it.

This is why the definitions matter. HFMA's Net Days in A/R uses AR net of contractual allowances, divided by average daily net patient service revenue. The AAFP's version for practices divides total receivables by average daily charges. Either works if you stay consistent, but an AR total that still carries contractual adjustments looks bigger, and older, than the money you can actually collect.

AR is sorted into buckets by how long each balance has been open. HFMA uses 0-30, 31-60, 61-90, 91-120 and over 120 days, aged from the date of service for physician practices. Some billing systems age from the date the claim was billed instead, so check which one your report uses: the gap between the two is your billing lag.

For a benchmark, the AAFP's guidance for practices is that days in A/R should stay below 50 at minimum, and 30 to 40 is preferable. It also warns that the average can look fine while the old end of the report does not:

That is why the share of AR over 120 days is tracked on its own.

Here is the trouble with working AR by bucket. The buckets count days since the date of service. The deadlines that decide whether a claim can still be paid run on other clocks, and the payer sets them:

• Original Medicare filing: a claim must be filed within 1 calendar year of the date of service (42 CFR 424.44).
• Texas Medicaid filing:claims to the acute care program must be received within 95 days of each date of service (1 Tex. Admin. Code § 354.1003).
• Original Medicare appeals: a redetermination request is due 120 days after you receive the denial notice, and the notice is presumed received 5 days after its date (42 CFR 405.942).
• Commercial plans:whatever your contract says. UnitedHealthcare's 2026 administrative guide does not publish a filing limit at all; it says limits vary by state and contract and sends providers to their agreement.

Put four claims from the same AR report on one axis and switch the order. Gray is time already gone. Blue is time left before the deadline that applies to that claim.

Oldest first, the two Medicare claims lead, and both sit in the over-120 bucket that every benchmark flags. Fewest days left first, the Texas Medicaid claim jumps to the top. It is in the 61-90 bucket, it has 15 days before it can never be paid, and nothing on the aging report says so. The Medicare claim that never reached the payer is 200 days old and still has 165.

The follow-up itself is the same handful of steps every team knows. What changes is the order you take the claims in.

• Confirm the payer has it.A claim status inquiry (the X12 276/277 transaction, or the payer's portal) tells you whether the claim was received, is pending, or was never there.
• Read the remit. The 835 carries the reason codes that say what happened to each line.
• Route each denial by its code to a corrected claim, an appeal or a reprocessing request. The denial-to-appeal walkthrough covers which codes go where.
• Post payments and adjustments. Contractual adjustments come off AR. They are not denials and should not sit in a denial queue.
• Move the patient's share to patient AR and bill it.
• Write off what is truly gone, with the reason, so the aging report stops carrying it.

Yeam's worklist is built on the second ordering. Drop in a denied-claims export and each denial comes back with its remedy and the days left to file, soonest deadline first. Contractual adjustments like CO-45 are treated as write-offs, so they never inflate what the worklist calls recoverable. It runs in your browser and nothing is uploaded. Try it on your own export.

• 42 CFR 424.44, Time limits for filing claims (Original Medicare)
• 42 CFR 405.942, Time frame for filing a request for a redetermination
• 1 Tex. Admin. Code § 354.1003, Time limits for submitted claims (Texas Medicaid)
• X12, Claim Adjustment Reason Codes (CARC 1, 2, 3 and 45)
• 45 CFR 162.1402, Standard for the health care claim status transaction (276/277)
• HFMA, MAP Keys, 2023 Edition (AR-1 aged A/R, FM-1 net days in A/R)
• AAFP, Practice finances (days in A/R, A/R over 120 days)
• UnitedHealthcare, 2026 Care Provider Administrative Guide (timely filing, processing time)

Last checked Nov 1, 2026. Filing limits and appeal windows differ by payer, plan type, state and contract. Check the one that governs your claim before relying on any number here.