# What is an alert threshold?

> An alert threshold is the value that makes an ad alert fire, such as cost per lead over INR 455. How to set one from a baseline and a buffer, with an example.
- **Author**: Marxx
- **Published**: 2026-11-07
- **Category**: Alerts
- **URL**: https://marxx.ai/library-glossary/alert-threshold

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An alert threshold is the value that makes an alert fire, such as "cost per lead over INR 455" or "CTR down 25%". Set it too tight and the alert fires on normal days. Set it too loose and it stays quiet while money leaks.

## The formula

Threshold = baseline x (1 + buffer)

The baseline is your normal value, usually the average over the last 30 days. The buffer is the swing you accept as normal. For metrics where lower is worse, such as CTR, the threshold sits below the baseline: baseline x (1 − buffer).

## A worked example

Say Palm Crest Homes runs Meta lead ads for flats in Pune.

1. Last 30 days: INR 42,000 spent for 120 leads. Baseline cost per lead = INR 42,000 / 120 = INR 350.
2. Buffer: 30%.
3. Threshold = INR 350 x 1.3 = INR 455.
4. The alert fires when any ad set's cost per lead goes over INR 455 in the last 3 days.

For CTR: the baseline is 1.2%, the buffer is a 25% drop, so the threshold is 1.2% x 0.75 = 0.9%.

## Fixed and relative thresholds

| Type | Example | Good for | Watch out |
|---|---|---|---|
| Fixed number | Cost per lead over INR 455 | Costs with a clear target | Needs updating when targets change |
| Change against the past | CTR down 25% vs previous 7 days | Rates that differ by ad | Can fire on a small base |
| Zero check | Spend over INR 1,000 with 0 results | Broken forms or tracking | Needs a sensible spend floor |

Pair each threshold with a minimum spend, so an ad set that spent INR 300 cannot trigger it.

## What good looks like

A good threshold fires when someone would want to act, and rarely otherwise. If more than half its alerts lead to no action, widen it. If you keep finding problems it missed, tighten it. See [CPA](/glossary/cpa) and [CTR](/glossary/ctr) for the metrics behind the common ones.

We make Marxx. Its alerts compare a metric with your threshold over a window and show both numbers, as in "Cost per result 1,420 > 900 (last 3 days)". See [Meta ads alerts in Slack](/guides/how-to-set-up-meta-ads-alerts-in-slack).

## FAQ

### What buffer should I use?

Start around 30% to 50% for costs and 20% to 30% for rates like CTR. Adjust after two weeks of real alerts.

### Should a threshold use my target or my average?

Use the target for a new account. Use the 30-day average once results are steady, so the alert flags change from normal.

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- [More Alerts articles](https://marxx.ai/library-glossary/category/alerts)
- [All articles](https://marxx.ai/library-glossary)