Practitioner tool
Rolling 12-Month Limit Tracker
“Are we going to bust a 12-month rolling limit, and how much room is left next month?”
1. Set up the limit
Your permit condition defines the limit, the window, and whether it is a sum or an average. Enter them exactly as written. Data stays in this browser.
2. Enter monthly values
Copy a column of monthly values (or month and value columns) from Excel and paste here. Blank cells count as missing months.
Forecast (optional)
Add planned months to see when the rolling value would cross the limit.
3. Results
- Rolling total, Month 12
- — tons
- Enter a limit to compare
- Headroom for Month 13
- —
- Enter a limit
- Windows over the limit
- 0
- 0 at or above the alert level
- Forecast
- None set
- Add planned months above
The chart appears once there are at least two full windows.
| Month | Value (tons) | Rolling total | % of limit | Status |
|---|---|---|---|---|
| Month 1 | — | —(0 mo) | — | Building window |
| Month 2 | — | —(0 mo) | — | Building window |
| Month 3 | — | —(0 mo) | — | Building window |
| Month 4 | — | —(0 mo) | — | Building window |
| Month 5 | — | —(0 mo) | — | Building window |
| Month 6 | — | —(0 mo) | — | Building window |
| Month 7 | — | —(0 mo) | — | Building window |
| Month 8 | — | —(0 mo) | — | Building window |
| Month 9 | — | —(0 mo) | — | Building window |
| Month 10 | — | —(0 mo) | — | Building window |
| Month 11 | — | —(0 mo) | — | Building window |
| Month 12 | — | — | — | Missing month |
How this works
The math
- Each month's rolling value is the sum (or average) of that month and the months before it, for the window length you set.
- A window is flagged over the limit only when its value is above the limit you entered; equal to the limit is not over.
- Next-month headroom is the limit minus the most recent months that will still be in next month's window. For an average limit, it is the limit times the window length minus that sum.
- Months with no value are treated as missing data, and any window that contains one is flagged instead of being compared.
Using it on a real permit
- Enter the limit, window, and units exactly as the permit condition states them, and use the same units for every month.
- Monthly values should be the figures you would put in the record: calculated emissions, metered throughput, fuel use, or hours.
- Set the alert level where you want time to react; many teams watch the forecast as well as the alert.
- Export the CSV as a working record. Your permit's recordkeeping condition decides what must be kept and for how long.
AirPermitHub provides educational, engineering, research, and compliance-support information. Information provided by the platform does not constitute legal advice and should not replace review of applicable regulations, permits, agency guidance, or consultation with qualified professionals. Full disclaimer