When you see ↑ 50% vs last month or ↓ 67% vs last month on your stats cards, that percentage is calculated by comparing two calendar months — not a rolling 30-day window.
Calendar months, not rolling windows
This month = from the 1st of the current month until now
Last month = the entire previous calendar month
So if today is May 14:
- "This month" = May 1 – May 14
- "Last month" = April 1 – April 30
This is the same approach used by most analytics and billing platforms. It aligns with how teams and businesses naturally think about reporting periods.
Why a recent email can count as "last month"
If an email arrived 23 days ago and today is May 14, that email arrived on April 21 — which falls in last month's window, not this month's.
The gap in days doesn't matter. What matters is which calendar month it landed in.
How the percentage is calculated
The formula is straightforward:
trend = ((this month - last month) / last month) × 100
Examples:
| This month | Last month | Result |
|---|---|---|
| 4 | 12 | ↓ 67% |
| 15 | 10 | ↑ 50% |
| 0 | 0 | — 0% |
| 3 | 0 | ↑ 100% |
The 100% case happens when you had no activity last month but have some this month. There's no last month baseline to calculate from, so it shows 100%.
What "— 0% vs last month" means
This shows when:
- Both months had the exact same count, or
- Both months had zero activity
It doesn't mean something is wrong — it just means activity was consistent or absent across both months.