Compare against previous period

Last updated: May 19, 2026

Compare against previous period

Date picker → toggle "Compare to" → pick previous period (same days last week / month / year / custom). All metrics show delta (% change) vs the comparison. Useful for WoW + MoM + YoY analysis. Caveat: seasonal effects make "same days last year" more meaningful than "same days last month" for seasonal businesses.

Who is this for

Mediabuyers running weekly / monthly reviews. Anyone comparing this period to a baseline to spot trends.

How to enable comparison

Step 1: Set base date range

In date picker, pick your current period (e.g. "Last 7 days").

Step 2: Toggle Compare to

In date picker, click Compare to toggle.

Step 3: Pick comparison period

Options:

Comparison

What it picks

Same days previous period

Equal-length window immediately before base (e.g. Last 7 days = 8-14 days ago)

Same days last week

Equal-length 7 days earlier (for daily/weekly cycles)

Same days last month

Equal days in previous calendar month (e.g. 1-7 of last month vs 1-7 this month)

Same days last year

Equal days 365 days ago (seasonal comparison)

Custom

Pick specific dates for the comparison

Step 4: Apply

Click Apply. Metrics now show:

  • Current value

  • Comparison value (in smaller text)

  • Delta as % change (color-coded: green positive, red negative)

Example: ROAS 3.2 (+15% vs 2.8 prev)

Common comparison patterns

WoW (Week-over-Week)

  • Base: Last 7 days

  • Compare to: Same days last week (8-14 days ago)

  • Spot week-to-week trends

MoM (Month-over-Month)

  • Base: Last month full

  • Compare to: Previous month

  • Or: Same days this month vs same days last month (for partial-month comparison)

YoY (Year-over-Year)

  • Base: Last month or quarter

  • Compare to: Same period last year

  • Critical for seasonal businesses (e-commerce: Black Friday vs Black Friday last year)

Custom: pre/post event

  • Base: 7 days after product launch

  • Compare to: 7 days before launch

  • Measures launch impact

Where comparison shows

Ads Manager rows

Each metric column shows:

  • Current value

  • Below: delta % (green up, red down)

  • Hover for absolute change

Dashboard KPI strip

Top of dashboard:

  • Each KPI shows current + delta

  • Some show sparkline mini-chart for trend

Reports

CSV + PDF exports include columns for current + previous + delta (if comparison enabled at export time).

Seasonal interpretation

For seasonal businesses (e-commerce, travel, retail):

  • WoW: less meaningful (one off-week distorts)

  • MoM: somewhat meaningful (general trend)

  • YoY: most meaningful (same seasonal context)

Don't expect December's "MoM vs November" to look "normal" — December is its own animal. YoY for accurate read.

Combining with filters

You can apply filters + comparison:

  • Filter to ROAS < 1.5 underperformers

  • Compare to: same days last week

  • See: are the same campaigns underperforming, OR has the bad performance shifted to new ones?

Comparison in reports + exports

When you export with Compare to enabled:

  • CSV: includes columns current_*, previous_*, delta_* per metric

  • PDF: side-by-side or stacked charts for both periods

Useful for stakeholder reports: not just current state, but trend.

What delta colors mean

Color

Meaning

Green

Improvement (depends on metric — see below)

Red

Decline

Grey / no color

< 1% change (noise)

Bold green / red

> 25% significant change

Metric-specific:

  • Higher better: ROAS, conversions, CTR → green for up

  • Lower better: CPA, CPM, frequency → green for down

UI handles this correctly (color reflects "good change", not just numeric direction).

Limits

  • One comparison at a time: can't compare to 2+ periods simultaneously (current vs last week vs last year). Export both separately.

  • Equal-length windows: comparison period auto-matches base length. Custom for unequal (less meaningful).

  • Time aggregation: per-day metrics + per-day comparison work; per-hour comparison less commonly supported.

Late attribution affects comparison

Recent periods (last 24-48h) have less-settled data than older. So comparing "Last 7 days" vs "Same days last week":

  • Last 7 days: Day 1 settled, Day 7 still settling

  • Previous week: fully settled

Delta may look worse than reality for current period. Re-check after 3-7 days for stable comparison.

What you'll see

Date picker with Compare to enabled:

  • Two date chips side-by-side: current + comparison

  • Metric cells show both values

  • Delta in % with color

  • Hover: tooltip with absolute change + comparison details

Common questions

  • "Comparison shows +500% — is that real?": small baseline → big % swings. Check absolute numbers; 1 → 6 = +500% but small impact.

  • "Why does compare to last year look weird?": workspace may not have had data 1 year ago (new account). Comparison requires data in both periods.

  • "Can I compare two custom periods?": yes — pick "Custom" in Compare to → enter dates.

  • "Compare across platforms shows odd deltas": platform mix may have changed (you added a new platform). Filter to consistent platform set.

  • "Comparison metric absent in CSV export": ensure Compare to enabled at export time + Include comparison columns toggle ticked.

Best practices

Use YoY for seasonal

Q4 2026 vs Q4 2025 (not Q4 vs Q3) for ecommerce.

Watch for new factors

If you scaled budget 3x between periods: ROAS likely dropped. Comparison should account for budget scale.

Track delta over time

Don't just look at this week's delta. Track delta-of-delta:

  • Last week ROAS: +15%

  • This week ROAS: +5%

  • Trend: improvement slowing

Reconcile annually

For YoY comparisons: account for changes (new audience added, new platform, etc.). Pure YoY may be apples-to-oranges.

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