Glossary / Length of need
Length of need Medicare DME termLength of need
The practitioner's estimate, in months, of how long the patient will need an item; 99 meant lifetime on the retired CMN forms. Optional on the SWO.
Length of need (LON) is the treating practitioner's estimate of how many months the patient will need a DMEPOS item. It was a required field on the Certificates of Medical Necessity that CMS retired at the start of 2023, where the entry was a number from 1 to 99 and 99 meant lifetime. Suppliers and billing systems still use that convention.
Under the 2020 Standard Written Order rule, length of need is not one of the required order elements. The DME MACs say it may be beneficial to include, and that anything added to the order has to be supported by the medical record. If a coverage policy needs a length of need for a claim decision, reviewers look to the clinical notes rather than to the order.
Where LON still matters is rental equipment and continued-use reviews. Capped rental items such as CPAP and hospital beds are billed monthly, and the record needs to show that the need continues over that period. A stated length of need on the order and a matching statement in the notes make that easy to demonstrate.
Common questions
Is length of need required on the SWO?
No. The six required elements are name or MBI, order date, item description, quantity, practitioner name or NPI, and signature. LON is optional but often useful.
What does 99 mean?
Lifetime. The retired CMS-484 oxygen CMN labeled the field as 1 to 99 months with 99 equal to lifetime, and the convention has outlived the form.
Should I still put a length of need on rental orders?
It is optional, but AffirmDME's checklist flags a rental item with no stated length of need as a conservative practice, so the duration of need is documented somewhere in the file before you bill.
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Sources: 42 CFR 410.38(d) — Standard Written Order elements · Noridian: Understanding Standard Written Order Requirements · CMS-484 Oxygen Certificate of Medical Necessity (retired form) . Definitions summarize public Medicare policy and are not legal or billing advice.
More terms
- ADR — Additional Documentation Request
- Prior authorization
- Affirmation and non-affirmation
- UTN — Unique Tracking Number
- SWO — Standard Written Order
- Face-to-face encounter
- DME MAC — Durable Medical Equipment Medicare Administrative Contractor
- Jurisdiction
- PTAN — Provider Transaction Access Number
- NPI — National Provider Identifier
- MBI — Medicare Beneficiary Identifier
- LCD — Local Coverage Determination
- NCD — National Coverage Determination
- Policy article
- HCPCS — Healthcare Common Procedure Coding System
- Prior authorization exemption
- Competitive bidding
- CMN and DIF — Certificate of Medical Necessity and DME Information Form
- Proof of delivery
- TPE — Targeted Probe and Educate
- Prepayment review