How Amplitude handles simultaneous events in a funnel
Amplitude rounds all time to the nearest second. For that reason, it maintains a one-second window to account for simultaneous events. If a user fires two different events within one second, Amplitude doesn't try to determine which one came first. Instead, it considers either order correct and applies that to your funnel.
For example, if a user fires Event B first, and then fires Event A within one second, a funnel counts this as a conversion from either Event A -> Event B, or Event B -> Event A.
In an exact order funnel, if an event that isn't part of your funnel definition fires simultaneously in the same second, Amplitude still considers that user converted.
When you use Historical Count filters on the same events that occur within the same second, users appear to have dropped off. The funnel query doesn't distinguish between events that happen within the same second, but the Historical Count filter does.
Same events fire at once
If two of the same event types send within the same second, Amplitude counts only one of them. This also applies if you use Any Event within the step of a funnel, or if custom events within your funnel steps share the same sub-events: Amplitude assumes they're the same event if they fire at the same second and doesn't count each instance. To address this, ensure the step conditions are mutually exclusive, or turn on millisecond resolution to capture events precisely.
Millisecond resolution
By default, Amplitude assumes events don't trigger within one second of each other. However, if you have multiple events that fire at the same time and you want to observe the precise order of events, you can turn on millisecond resolution.
Follow these steps to track events by the millisecond:
- From your Funnel Analysis, open the Advanced dropdown in the Measured As module.
- Click Millisecond resolution.
The funnel updates automatically, and shows events tracked by the millisecond instead of by the second.
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