What is the difference between a reopening and a redetermination?

A reopening fixes an error in a claim Medicare already processed, usually a clerical mistake such as a wrong code or date. A redetermination is the first level of appeal, used when you disagree with Medicare's decision itself. They have different deadlines, and asking for one does not pause the clock on the other.

Is a corrected claim the same as a reopening?

They do the same job at different payers. Most commercial payers take a replacement claim with frequency code 7 and the original claim number. Medicare contractors generally handle corrections to a processed claim through a reopening instead, so check your contractor's guidance for the claim type you bill.

How long do I have to file a Medicare redetermination?

120 calendar days from the day you receive the initial determination, and receipt is presumed to be 5 calendar days after the date on the notice. A contractor can extend the deadline for good cause, but that is not something to plan around.

Can I appeal a claim that was rejected as unprocessable?

No. A claim returned as unprocessable never received a decision, so it has no appeal rights and there is nothing to reopen. Correct it and send it again as a new claim within the timely filing limit.

What happens if my reopening request is refused?

You cannot appeal the refusal itself, but you can still appeal the original denial if its deadline has not passed. That is why the appeal deadline should be tracked from the day the denial arrives, not from the day the reopening is refused.

Reopening vs redetermination vs corrected claim: which one to file

A corrected claim, a reopening, and an appeal fix three different problems, and sending the wrong one can cost months. Two questions decide it. First, did the payer decide the claim at all, or bounce it back as unprocessable? A claim that was never decided has no appeal rights: fix it and send it again as a new claim. Second, for a claim the payer did decide, was the problem your billing mistake, or do you disagree with the decision? Your own error - a transposed code, wrong units, a missing modifier - takes a correction: a reopening at Medicare, a corrected claim at most other payers. A decision you think is wrong, such as a medical necessity or coverage denial, takes an appeal: a redetermination at Medicare, a reconsideration elsewhere.

How to decide

1
Check whether the claim was decided at all
A claim rejected at the front end, or returned as unprocessable, never got a decision - at Medicare it comes back with remark code MA130. There is nothing to reopen or appeal. Correct it and send it as a new claim, inside the payer's timely filing limit.
2
If it was decided, work out whose problem it is
An error in what you billed - the wrong code, units, dates, or modifier, or a digit typed in the wrong order - is yours to correct. A decision you think is wrong on the merits - not medically necessary, not covered, bundled when it should not be - is the payer's to reconsider.
3
Fix your own error with a correction
At Medicare that is a reopening: minor errors and omissions on a processed claim are handled as reopenings, not appeals. At most commercial payers and many Medicaid plans it is a corrected claim - a replacement claim with frequency code 7 that carries the original claim number.
4
Dispute the payer's decision with an appeal
At Medicare the first level is a redetermination by the contractor that processed the claim. Other payers call it a reconsideration, a claim review, or a first-level appeal. Either way, send the records that support your position, not just a request to look again.
5
Check the clock before you send anything
Each route has its own deadline, and they run at the same time rather than one after another. Write down the appeal deadline the day the denial arrives, even if you plan to try a correction first.

The three routes side by side

New claim

Use it when: The payer never decided the claim - it was rejected or returned as unprocessable.
Medicare: Correct the claim and submit it again as a new, original claim.
Most other payers: The same: a new, original claim, not a replacement.
Watch out: The timely filing limit still runs from the date of service, so a rejected claim that sat in a queue can expire before it is resent.

Correction

Use it when: The payer decided the claim, and the problem was an error in what you billed.
Medicare: A reopening, requested from the contractor that processed the claim.
Most other payers: A corrected claim: frequency code 7 with the original claim number, or code 8 to void the original.
Watch out: A corrected claim sent without the replacement code and original claim number looks like a second copy and is likely to deny as a duplicate.

Appeal

Use it when: The payer decided the claim, and you disagree with the decision itself.
Medicare: A redetermination - the first of Medicare's five appeal levels.
Most other payers: A reconsideration, claim review, or first-level appeal, per the payer's process.
Watch out: An appeal is the wrong tool for your own typo: it takes longer, and at Medicare a clerical fix belongs in a reopening.

Medicare deadlines

Each window below is set by federal regulation or CMS guidance, linked beside it. They run at the same time, not one after another.

Redetermination: 120 days
120 calendar days from the day you receive the initial determination. Receipt is presumed to be 5 calendar days after the date on the notice unless shown otherwise.
42 CFR 405.942 - Time frame for filing a request for a redetermination
Redetermination decision: 60 days
The contractor generally has 60 calendar days from receiving a timely request to decide it.
42 CFR 405.950 - Time frame for making a redetermination
Reopening for any reason: 1 year
Within 1 year of the date of the initial determination or redetermination.
42 CFR 405.980 - Reopenings of initial determinations and redeterminations
Reopening for good cause: 4 years
Within 4 years, when there is new and material evidence that was not available before, or the record shows an obvious error.
42 CFR 405.986 - Good cause for reopening
Reopening to fix a clerical error: any time
When an unfavorable decision rests on a clerical error, you can ask for a reopening to correct it at any time. A mistake made by another payer does not count as a clerical error.
42 CFR 405.980 - Reopenings of initial determinations and redeterminations
New claim: 1 year from the date of service
A claim must reach Medicare within 1 calendar year after the date of service, which is the window a rejected claim has to be fixed and resent in.
42 CFR 424.44 - Time limits for filing claims

Commercial and Medicaid deadlines

Windows for corrected claims, reconsiderations, and appeals at commercial payers are set by each contract, and Medicaid windows by each state, so they vary too much to state here. Look up the specific payer before you file, and treat its own provider manual as the final word.

Browse payer billing references

Where the wrong choice costs months

A reopening request does not stop the appeal clock
Asking for a reopening does not extend the time to file an appeal. If the contractor declines the reopening after your 120 days have run, the redetermination route may be gone too.
CMS MLN Matters MM4147 - Clerical errors handled as reopenings
A refused reopening cannot be appealed
Whether to reopen is the contractor's call, and that decision is final. You can still appeal the original denial - but only while its own deadline is open.
42 CFR 405.980 - Reopenings of initial determinations and redeterminations
Appealing an unprocessable claim burns the filing window
A claim returned as unprocessable has no decision to appeal, so the request goes nowhere while the timely filing limit keeps running. Fix it and send a new claim instead.
Medicare Claims Processing Manual (Pub. 100-04), Chapter 1 - unprocessable claims
A pending appeal can take a reopening off the table
Once a valid appeal is open on an issue, the contractor generally can no longer reopen the claim on that same issue. Choose the route before you file, not after.
Medicare Claims Processing Manual (Pub. 100-04), Chapter 34 - reopenings

Common denials and the usual route

CO-16 Claim or service lacks required information. Read the remark code first. Returned as unprocessable, it needs a new claim; a field you got wrong on a processed claim needs a correction.
CO-18 Exact duplicate claim or service. Do not send it again. Check whether the original paid or is still pending, and change it with a correction rather than a second original.
CO-4 The modifier does not match the procedure code billed. A correction when the modifier was simply wrong; an appeal when the modifier was right and the payer still disagrees.
CO-97 Service is bundled into another service already adjudicated. A correction when a modifier that legitimately unbundles the service was left off; an appeal when you dispute the bundling itself.
CO-50 Not deemed medically necessary by the payer. An appeal, with the records that show why the service was medically necessary for this patient.

Frequently asked questions

What is the difference between a reopening and a redetermination?: A reopening fixes an error in a claim Medicare already processed, usually a clerical mistake such as a wrong code or date. A redetermination is the first level of appeal, used when you disagree with Medicare's decision itself. They have different deadlines, and asking for one does not pause the clock on the other.
Is a corrected claim the same as a reopening?: They do the same job at different payers. Most commercial payers take a replacement claim with frequency code 7 and the original claim number. Medicare contractors generally handle corrections to a processed claim through a reopening instead, so check your contractor's guidance for the claim type you bill.
How long do I have to file a Medicare redetermination?: 120 calendar days from the day you receive the initial determination, and receipt is presumed to be 5 calendar days after the date on the notice. A contractor can extend the deadline for good cause, but that is not something to plan around.
Can I appeal a claim that was rejected as unprocessable?: No. A claim returned as unprocessable never received a decision, so it has no appeal rights and there is nothing to reopen. Correct it and send it again as a new claim within the timely filing limit.
What happens if my reopening request is refused?: You cannot appeal the refusal itself, but you can still appeal the original denial if its deadline has not passed. That is why the appeal deadline should be tracked from the day the denial arrives, not from the day the reopening is refused.

Rules last checked against the cited sources on October 26, 2026.

Medicare rules here are plain-English summaries of the regulations and CMS guidance linked above, written for reference and not legal advice. Your Medicare contractor, state Medicaid program, or commercial payer contract has the final word on how a specific claim is handled.