Why Your Impressions Dropped

The short version

Impressions fall for exactly three reasons:

You stopped bidding — budget exhausted, schedule ended, something paused, billing failed.
You stopped winning — the auction got more expensive or your bid constraint got tighter.
You ran out of people — the audience is exhausted or shrinking.

They look identical on a chart and need completely different responses, so identify which one before changing anything.

1. Did you stop bidding?

Check this first because it is free and it is often the answer.

Budget exhausted earlier in the day than usual, so the tail of the day has no delivery.
A schedule or end date passed.
Something upstream paused — the campaign, the ad set, or the ad.
Billing failed or an account spending limit was reached.
An ad was rejected and you did not notice.

A sharp cliff to near-zero usually means this category. Gradual decline usually does not.

2. Did you stop winning?

If you are still bidding and still getting nothing, you are losing the auction.

Something on your side changed. A lowered bid cap, a tightened cost cap or target, a reduced budget. Automated bidding will serve nothing rather than violate a constraint, and that is intended behavior rather than a fault.

Something on their side changed. More competitors, a seasonal peak, a large advertiser entering your audience. CPM rising while impressions fall is the signature.

The distinguishing check: did CPM rise? If yes, the auction changed. If CPM is flat and impressions fell, the constraint is yours.

3. Did you run out of people?

The slowest and most easily missed cause.

Frequency rising while impressions fall means you are reaching the same shrinking group more often.
Retargeting pools shrink when upstream traffic falls, so a retargeting campaign can decay because a prospecting campaign was reduced weeks earlier.
Exclusions accumulate. Every purchaser excluded permanently is one fewer person available.

This one usually has a cause somewhere other than the campaign showing the symptom.

The shape of the drop tells you a lot

Cliff to zero. Something stopped: budget, billing, approval, schedule.

Step down to a lower plateau. A setting changed, or a competitor arrived and stayed.

Gradual decay over weeks. Audience exhaustion or creative fatigue.

Daily pattern that ends early. Budget exhausting before day end.

What not to do

Do not raise the budget before confirming you can spend the current one. If you are not winning, more budget buys nothing.
Do not duplicate the campaign. That adds a competitor for your own audience and a second thing to diagnose.
Do not treat a weekend or holiday dip as a trend.

Practical rule

Check whether you are still bidding, then whether CPM moved, then whether frequency rose. Those three answers separate the three causes, and each one has a different fix.