# Comparing email results over time without fooling yourself

> This week against last week can mislead you. Compare like with like: whole weeks, the same number of sends and the same season last year.

By The Wizel Team · Published 2026-10-01

“Revenue is down 20% on last week” sounds alarming until you notice last week had a sale and this week didn't. Many bad calls in email reporting come from comparing two periods that were never alike.

## Compare like with like

**52 weeks** back: the same week last year is the fairest comparison for a seasonal business

- Use whole weeks. Comparing a Monday to Wednesday with the previous Thursday to Saturday mixes up weekday habits.
- Match the number of sends. Three campaigns this week against one last week tests your volume, not your emails.
- Mark promotions and launches. Compare a sale week with your last sale week, not with a quiet one.
- Keep settings fixed. If your attribution window changed between the two periods, the numbers aren't comparable.

## Account for the season

Most stores have a rhythm across the year. November and December lift most retail stores, January often dips, and each category has its own peaks: swimwear before summer, candles as the nights draw in, gifts before holidays. Comparing October with November will almost always flatter November.

That's why year-over-year comparisons are so useful. The same weeks last year carry the same season, so the difference is closer to what you actually changed: your list, your offers and your emails.

## Read rates alongside totals

If revenue rose because you sent twice as many emails, revenue per recipient tells you whether each send got better or worse. If revenue rose while revenue per recipient held steady, you sent more of the same. Both can be fine. They just lead to different next steps.

> Before you react to a change, ask: same days, same number of sends, same season, same settings? If any answer is no, fix the comparison first.

## Ask your own numbers in Wizel

With Klaviyo connected, the Wizel chat runs these comparisons for you:

- “Compare the last 7 days with the previous 7 days.”
- “How did last month compare to the month before?”
- “Compare this year's Q4 to last year's Q4.”

## FAQ

### Is week-over-week or year-over-year better for email?

Use week-over-week to catch sudden problems, like a broken flow or a drop in deliverability. Use year-over-year to judge real progress, because it compares the same season.

### What if I don't have a full year of data yet?

Compare with the same weeks last quarter and mark any sales or launches in both periods. Your comparisons get much more reliable once a full year is in.

### Why did revenue fall when my open rate went up?

Opens and revenue measure different things, and Apple Mail Privacy Protection can lift opens without anyone reading. Check click rate and revenue per recipient, and whether a sale ran in the earlier period.

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Source: Wizel (https://www.wizel.ai/blog/compare-email-results-over-time)
Last updated: 2026-10-01