Personalized Send Time reports a lift. Here is what it is measured against

Klaviyo’s Personalized Send Time sends each recipient a campaign at their predicted best time inside a delivery window you set, and reports the lift of the personalized group over a control group. Before that lift goes in a client report, check what it was measured against.

The feature is on the Marketing Analytics and Advanced Klaviyo Data Platform packages, for campaigns only. For each campaign that uses it, “a randomly selected portion of eligible recipients is automatically held out in a control group”, and the control group’s size “is automatically managed by Klaviyo and may change over time; you do not need to configure or maintain it”.

Control recipients still get the campaign, on a schedule you choose between two options. Historical send time, which Klaviyo recommends, is picked “automatically based on your account’s past send performance”. The other is a fixed time you set, localized to each recipient’s time zone.

Lift is “the relative difference between the Personalized Send Time group and the control group for a given metric”, reported for open rate, click rate and placed order rate. Results appear once a campaign has been finished for at least 48 hours. There is a per-campaign view and an aggregate view, and the aggregate groups campaigns that used the same control send time. Open and click rates exclude bot activity, including Apple Mail Privacy Protection opens and automated bot clicks.

Which control the account used. Under historical send time, the lift says personalizing beat a time Klaviyo picked from your past sends. Under a fixed time, the lift measures the feature against that one choice of time, so a large lift is partly a statement about the time you chose. The aggregate view groups campaigns by control send time, which is one place to see which option was in force. If it was a fixed time, say what the time was.

The rates on both sides. Lift is relative. A 10% lift in placed order rate on a campaign whose control converted 2% of recipients is a move from 2.0% to 2.2%, two more ordering recipients per thousand. Klaviyo’s page describes the lift and does not say whether each side’s rate is shown. Look for both rates in the campaign’s results view. If they are not there, the report says so.

Which metric. Open-rate lift excludes privacy opens, so it under-counts engagement from Apple Mail users, and Klaviyo does not say how the denominator is handled. Click rate excludes automated bot clicks the same way. Placed order rate has the smallest counts of the three, so a single campaign’s lift on it may fluctuate more than the others, and the control group’s size is a number Klaviyo sets and can change. That is the reason to report the aggregate rather than any one send.

The report entry

What we would put in the client report, as one entry. The acceptance rule at the end is ours; Klaviyo’s help page gives no rule for when a lift is worth reporting.

Personalized Send Time, October 2026. Control: historical send time (Klaviyo’s choice from past sends). If a fixed time was set, write the time instead. Campaigns in the aggregate view: 9, all October sends that used the feature with this control. Placed order rate: personalized 2.2%, control 2.0%; lift 10%. If Klaviyo’s view shows only the lift, write “rates not shown in Klaviyo’s view” in place of the two figures. Click rate: personalized 3.1%, control 2.9%; lift 7%. Open rate: not reported; Klaviyo excludes Apple privacy opens from this figure, so it is not comparable with the open rates elsewhere in this report. Reported because: the aggregate covers a full month of campaigns and the placed order lift and the click lift point the same way. A lift is left out of the report when either condition fails; a single campaign’s lift is never reported on its own. What this is not: a revenue figure. The feature changes when a message arrives, not what was ordered.

The figures are illustrative. The two sentences in the “reported because” line are the rule to keep.