90 Day Global Period Calculator: Find Your Exact Post-Op Billing Window
Enter a procedure date and its global period, and see the exact last covered day, the modifier that applies if care is needed again during the window, and a clear breakdown of what typically falls inside versus outside that period.
Set up your calculation
Runs entirely in your browser. Nothing entered here is stored, transmitted, or logged.
Use the actual date the procedure was performed. Under CMS rules, the day of surgery itself is always included as part of the global period, not counted separately.
This comes from the Medicare Physician Fee Schedule's global surgery indicator for that specific CPT code, not from the type of surgery alone. Two procedures that sound similar can carry different global periods, so always confirm the indicator on the current CMS fee schedule look-up tool before billing.
Choosing a scenario adjusts the recommendation box below to point you toward the modifier typically associated with that situation.
Your global period breakdown
Enter a procedure date and select a global period to see your result.
Common modifiers used inside a global period
| Modifier | Typically used for |
|---|
What a 90-day global period actually covers
A global surgery period is the window of time during which routine, related follow-up care after a procedure is bundled into the original payment for that surgery rather than billed separately. Under Medicare's Physician Fee Schedule, each CPT code carries a global surgery indicator, most commonly 000, 010, or 090 days, and that number tells you exactly how many days of post-operative care are already included in the reimbursement for the procedure itself. This 90 day global period calculator exists because manually counting that window, and remembering which modifier applies if something else happens during it, is one of the more common sources of billing errors in a surgical practice.
Getting the end date right matters for more than just curiosity. Billing for an unmodified follow-up visit that actually falls inside the global window is a frequent cause of claim denials, while forgetting to apply a modifier for a genuinely separate or unrelated service during that same window can mean leaving money on the table that was properly billable.
How the calculation works
The math itself follows standard Gregorian calendar counting, consistent with international date standards like ISO 8601, applied the way CMS defines a global period: the day of surgery counts as day zero, and the global period then runs for the full length assigned to that CPT code, with the last day of the window falling on day 90 for a 90-day global period, day 10 for a 10-day period, or the day of surgery itself for a 0-day period.
Why the global period length isn't tied to the surgery type alone
It's tempting to assume "major surgery equals 90 days" and "minor procedure equals 10 or 0 days," and that's usually a reasonable starting assumption, but the actual global period is assigned per CPT code on the Medicare Physician Fee Schedule, and it can differ from what intuition suggests. The safest approach is always to look up the specific CPT code's global surgery indicator directly rather than relying on the general category of the procedure.
Reading your result breakdown
Once you calculate, you'll see the exact end date of the global window front and center, a progress indicator showing how far into that window today's date falls, and a set of quick stats covering the total days remaining, the day-of-week the window closes on, and whether that closing date falls on a weekend. Below that, a modifier reference table and a scenario-based recommendation box point you toward the coding decision that typically applies to the situation you selected.
A quick worked example
Take a 90-day global procedure performed on a Wednesday. The global period runs through day 90, landing roughly thirteen weeks later. If the patient returns during week six for a routine wound check related to that same surgery, that visit is typically already covered by the global package and isn't separately billable. If instead the patient needs an unplanned trip back to the operating room during that same week for a complication, that return trip is usually billed with a modifier indicating a related procedure during the post-operative period, rather than treated as routine follow-up.
Frequently asked questions
What is a 90 day global period in medical billing?
It's the 90-day window following certain major surgical procedures during which routine, related follow-up care is bundled into the original surgical payment rather than billed as a separate service, based on the global surgery indicator assigned to that CPT code.
Does the day of surgery count as day 1 or day 0 of the global period?
The day of the procedure itself is counted as day zero. The global period then extends for the full assigned length from that point, meaning a 90-day period reaches its last covered day on day 90 after the surgery date.
How do I know if a CPT code has a 0, 10, or 90 day global period?
The global surgery indicator is listed directly on the Medicare Physician Fee Schedule for that specific CPT code. Since two similar-sounding procedures can carry different indicators, checking the code directly is more reliable than assuming based on the type of surgery.
What modifier do I use for an unrelated procedure during someone's global period?
An unrelated procedure or service performed by the same physician during another procedure's post-operative period is commonly reported with a modifier indicating it's unrelated to the original surgery, so it can be considered for separate payment. The exact modifier depends on whether it's an evaluation and management service or another procedure.
What happens if a patient needs an unplanned return to the operating room during the global period?
An unplanned return to the operating room for a complication related to the original surgery is typically reported with a modifier specific to that situation, distinguishing it from routine included follow-up care and from a staged or planned second procedure.
Are global period rules the same in every country?
The global surgery package concept described here reflects the Medicare Physician Fee Schedule framework used in the United States. Other countries and private payers may define bundled post-operative windows differently, so always confirm against the specific payer's policy for care delivered outside the US Medicare system.
Related tools you might find useful
If you're tracking related dates, billing windows, or recovery timelines, a few other tools cover adjacent questions.
Recovering patients often ask about activity and energy levels too. The calories burned per day calculator is a useful companion for anyone easing back into movement during recovery, and the interest per day calculator comes in handy for anyone tracking finances during time off work.
This tool provides general educational information about how global surgery periods are typically counted and referenced in US Medicare billing. It is not billing, coding, or legal advice, and payer policies, CPT global indicators, and modifier rules can change. Always verify current global period assignments and coding guidance against the official Medicare Physician Fee Schedule and your payer's specific policy before submitting a claim.