Email send time

Carepatron marketing · 10 August 2026 · Customer.io data, Jan to Aug 2026
All days and times on this page are US Eastern unless labelled otherwise.

Tuesday or Thursday, 10:00 to 11:00 US Eastern. Never Sunday.

Low-risk default, not a proven winner. Timing is worth 2 to 3 points. Email type is worth 22.

Watch the timezone. Monday 9:00am Melbourne is Sunday 7:00pm US Eastern, which is the worst slot in the data. Scheduling by local AU/NZ time walks straight into it.

Timezone conversion

	US Eastern	Melbourne	Auckland
Send	Tue/Thu 10–11am	Wed/Fri 12–1am	Wed/Fri 2–3am
Avoid	Sunday, all day	Sun 2pm – Mon 2pm	Sun 4pm – Mon 4pm

August 2026 offsets (Melbourne +14h, Auckland +16h). These shift three times between September and November. Set the broadcast timezone in Customer.io to America/New_York and let it handle the changes.

Email type: the actual lever

Broadcast type	Sends	Human open
Product news	12	36.6%
Webinar	9	29.0%
Sales (Managed Billing)	4	25.6%
Offer / discount	42	14.0%

Median human open rate. 42 of 71 broadcasts were offers, so most of our volume sits on the bottom row.

Day of week

Day	Delivered	Human open	Human click
Monday	10,738	17.2%	1.71%
Tuesday	11,011	17.3%	1.61%
Wednesday	10,917	17.1%	1.47%
Thursday	9,729	17.8%	1.60%
Friday	9,103	17.6%	1.44%
Saturday	8,405	18.3%	1.65%
Sunday	9,200	16.1%	1.23%

69,103 campaign deliveries, 8 complete weeks. Best to worst is 14% relative on opens. Sunday is lowest on both measures. Saturday looking best is probably who signs up on weekends, not the day itself, so do not start sending Saturdays.

Time of day

Block (ET)	Sends	Human open
06:00 – 08:59	24	14.7%
09:00 – 11:59	34	22.7%
12:00 – 05:59	13	24.7%

This gap is not a time effect. Our offer emails go out at 7 to 8am and our announcements go out later. Compare like with like and it disappears: within offers only, the spread is 3.1 points (p = 0.28). Within webinars, mornings 29.2% and afternoons 28.5%.

Do this

Default to Tuesday or Thursday, 10–11am ET. Costs nothing and avoids sending at 4am Pacific.
Never schedule Sunday ET. Check the conversion table first if you are scheduling from Melbourne or Auckland.
Put the effort into offer emails. 14.0% against 36.6% for product news, across most of our volume.
Turn on Customer.io send-time optimisation. Times delivery per recipient instead of one global slot. Our US list spans four zones.
A/B test it if we want certainty. One recurring send, 08:00 vs 14:00 ET, identical content, six runs.

Caveats

Nothing here is causal. We never randomised send times.
Campaign send times track when users triggered the campaign, so day and hour partly reflect who those users are.
8 to 17 broadcasts per weekday, so only large effects would show up.
Human open rate undercounts on some clients even after stripping Apple Mail prefetch.

Method

Campaigns: 69,103 delivered, 8 complete weeks (14 Jun to 9 Aug 2026), campaigns 1, 73 and 3. Backfill blasts over 500 sends per hour excluded (3,311 messages).
Broadcasts: 71 email sends with 500+ delivered, 16 Jan to 21 Jul 2026, 423,830 delivered.
Both use Customer.io human_opened and human_clicked. Prefetch is roughly half of all recorded opens.
Audience is 66% US (PostHog signup location, last 90 days), so US Eastern is the frame.