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Need help in this area? See Methodology FAQ.
Utility bills rarely align with calendar months. A bill dated January 20 might cover December 21 – January 20. To give you consistent month-over-month reporting, Nectar converts your billing data into calendar month data — a process called calendarization.

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Why this matters

Without converting to calendar months, comparing energy use over time is difficult:
Raw billing dataCalendar month data
January bill: 10,000 kWh (covers Dec 21 – Jan 20)January: 3,500 kWh
February bill: 9,000 kWh (covers Jan 21 – Feb 18)February: 8,000 kWh
Hard to compare — different time periods overlapClean month-over-month comparison
Calendar month data is required for:
  • Year-over-year comparisons — comparing January 2024 to January 2023
  • ENERGY STAR reporting — requires data by calendar month
  • Budget tracking — budgets typically follow calendar months or quarters
  • ESG reporting — standard reporting uses calendar periods
Related docs: ENERGY STAR integration, Analytics overview

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How it works

Nectar spreads each bill’s usage evenly across its billing period, then calculates how much falls in each calendar month.

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Example

A bill shows 3,100 kWh covering January 15 – February 14 (31 days):
  1. Daily usage: 3,100 kWh ÷ 31 days = 100 kWh per day
  2. January portion: 17 days (Jan 15–31) × 100 kWh = 1,700 kWh
  3. February portion: 14 days (Feb 1–14) × 100 kWh = 1,400 kWh
Both the start and end dates are counted. A period from January 1–31 includes 31 days. This matches how utilities typically bill.

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Viewing the breakdown

Want to see exactly how your monthly totals are calculated? Use Inspect Aggregation on any site’s detail page:
  1. Go to Sites and select a site
  2. Click the Audit tab
  3. Select a month to see which bills contribute to that total
You’ll see:
  • Each bill’s original usage
  • How many days overlap with the selected month
  • The portion of usage attributed to that month
Related docs: Sites overview

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When multiple bills contribute

For most meters, a single bill contributes to two months (the one it starts in and the one it ends in). But sometimes multiple bills contribute to the same month: Example: Two bills for the same meter in January:
  • Bill A covers Jan 1–15 (500 kWh) → all 500 kWh goes to January
  • Bill B covers Jan 16–31 (600 kWh) → all 600 kWh goes to January
  • January total: 1,100 kWh

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Good to know

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This is an approximation

Calendarization assumes usage is spread evenly throughout the billing period. In reality, usage varies day to day. For most purposes — monthly reporting, year-over-year comparisons, budgeting — this approximation works well.

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Your original data is preserved

Nectar never changes your original bill data. Calendar month calculations happen when you view analytics or run reports. You can always see the original billing period data in your bill details.

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Costs work the same way

Costs are converted to calendar months using the same approach — spreading charges evenly across the billing period and allocating to each month based on the number of days.

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Next steps

Cost allocation

How costs are split when a bill covers multiple meters

Special situations

How Nectar handles revised bills and other complexities