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Most utility companies treat bill start and end dates in the same way. The day on which the meter is read is both the end date of the current bill and the start date of the next bill.

This makes sense because utility companies have historically read meters via an on-foot meter reading technician who walked from meter to meter and entered each reading into a hand-held device or ledger. Many meters have since advanced to remotely read systems using drive-by vehicles, pole-mounted data accumulators or other technologies. But regardless of the technology, the meter is read on a specific day and that single day is treated as both the end date of one billing period and the start date of the next.

Now that smart electric meters are becoming more common, some metering systems have the capability to compile, store and transmit detailed usage data on a “per day” basis, leading some bills to end at midnight on one day and the next bill to begin just after midnight on the next day. Also, some utility companies provide historical data in spreadsheet format in which the data has been manipulated to show calendar months, not billing periods.  For example, spreadsheet calendarized data may run March 1 to March 31, instead of March 1 to April 1. 

This topic will...

  • describe the rules in EnergyCAP regarding bill start and end dates
  • provide a case study to explain why the rules are needed

EnergyCAP, Inc. instituted a rule in 1982 that has remained unchanged since. Utility meters are assumed to be read at noon, so that the same day is both the end date of the current bill and the start date of the next.  A typical bill list illustrates this concept:


The start/end date day cannot be counted twice. For example, if March 30 was counted as both a March day and an April day, it would be counted twice, and the year would have 12 days too many. This would throw off the accuracy of use/day and cost/day calculations and hence affect audits, budgets and analytics.

The bill date rule says that utility meters are assumed to be read at noon, which means both the start date and end date are half days. To avoid confusion with half days vs. full days, the rule further states that the start day is counted as a full day and the end day is not counted.  Accordingly, looking at the above, the April billing period includes the full days of March 30 to April 29, a billing period length of 31 days (2 in March and 29 in April).

What happens when the vendor bills don’t end and start on the same day? Here’s an example:

You can see that the natural gas vendor bills its customer on a calendar month basis, setting the start date to be the day after the prior bill end date. Since EnergyCAP ignores the last day of the bill per the rule described above, each month has one day too few for purposes of use/day and cost/day calculations. (Curiously, the February bill starts on the same day as the January bill ended, so its day count is correct.)


Report BL08E with the Allowable Gap Days filter set to zero will catch these bills, showing a one-day gap for each.


In the above example the bills should be corrected by changing the end date to the first day in the next month, i.e. the August bill should be 8/1 to 9/1. The 9/1 end day is not counted in August, yielding a correct 31-day bill.

What are the ramifications of the above scenario in which the start date is the day after the prior end date?  The day count is one day too low, so use/day and cost/day calculations are about 3% too high.  Use/day and cost/day are used in a number of ways and may affect the accuracy of:

  • Audits
  • Calendarization and normalization
  • Budgets
  • PowerView charts
  • Reports
  • Accruals
  • Cost avoidance

Because any impact on cost avoidance reporting can affect energy savings performance, this topic will be discussed in detail.

  1. Impact when a baseline bill is affected.  If the end/start date rule is not followed in the baseline year, the baseline year will have 12 too few days. This will cause gaps in the baseline as shown by the CAP06 Baseline Report.


As a result, that “empty baseline” day will be set to no loss/no gain, which means the BATCC (baseline adjusted to current conditions) use and cost will be set to current, so that there is no use or cost avoidance for that day.  (Note: If any other special adjustments are in effect for that day, they will be taken into account after the BATCC use has been set to current, so any use and cost avoidance for the day will be the impact of special adjustments only, not the result of any energy use reduction from baseline.) Empty baseline days almost always result in slightly understated cost avoidance results for the month.


2. Impact when a current bill is affected.  If the end/start date rule is not followed in current bills, the impact on cost avoidance reporting is severe!

In this example, since the February end date doesn’t count, February 24 is missing. The user should have either entered February 25 as the end date of the February bill, or entered February 24 as the start date of the March bill. Either way, February 24 would then be counted.  



As a result, Feb 24 is not included in the adjusted baseline. The last day of the February calculations is February 23 and the first day of the March calculations is February 25.




Let’s assume that the day should have been added to March, which means that the March start date should have been February 24. 

With February 24 missing from the March calculations, the calculated cost avoidance is $1,067.  



But the BATCC use and BATCC cost are missing a full day, i.e. this day in essence has a zero baseline use and zero cost baseline as if the meter was not in operation on that day. This causes cost avoidance to be understated in all cases.

When the March bill start date is changed to February 24, that day now appears in the calculations which adds $149 to the adjusted baseline.


This corrects cost avoidance from $1,067 to $1,216, a change of 14% in this case.  


Note: You may ask how a one day change, about 3% of the month, can affect cost avoidance by 14% in this case. 

The change actually affects the adjusted baseline directly. You can see that BATCC cost increased by $148 from $4,183 to $4,331. The $148 correction represents 3.4% of the correct value of $4,331. This is a 29-day bill and 1/29 is 3.4%, so 3.4% is a reasonable upward correction of the adjusted baseline cost.  

But the actual March cost of $3,115 is not also corrected because that entire amount, all 29 days’ worth, was in the calculation the entire time. 

So the entire $148 correction increases bottom-line cost avoidance as can be seen in the equation in lower right above.  Since cost avoidance is about 25% of BATCC cost, the bottom-line impact is about 4x greater, or 14%.








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