Best time to send email campaigns: data and experiments

“Tuesday at 10 am” has been recycled through marketing blogs for a decade. The problem: your competitors read the same posts. Tuesday at 10 am is now the most crowded slot in the inbox. Here’s what the data actually shows, and how to find your own optimal window.

What the research says

GetResponse analyzed 4 billion emails sent in 2023-2024: the highest open rates fall on Tuesday (22.0%), Thursday (21.3%), and Wednesday (21.1%). Sunday is last at 17.8%. Opens peak between 9 and 11 am, with a smaller second peak from 1 to 3 pm.

Mailchimp, across hundreds of thousands of campaigns, confirms the pattern: weekdays beat weekends, mornings beat evenings. HubSpot adds: B2B peaks Tuesday-Thursday at 10-11 am; B2C tends toward Thursday and Friday, often closer to noon.

Campaign Monitor notes that 6-8 am sends produce the highest click rate (not just opens): someone checks email right after waking up and clicks immediately rather than setting the message aside. Omnisend, focused on e-commerce, puts Thursday and Tuesday at the top, with 8 am best for opens and 5 pm best for clicks. Their data shows Thursday promotional emails generated 12% more orders than the same emails sent on Monday.

Why “best time” varies by sender

All of this is a useful starting point. Treating it as gospel is a mistake. Here’s why.

Time zones. If your list spans Moscow and Vladivostok, “10 am” means two moments 7 hours apart. A send at 10:00 Moscow time arrives at 5 pm in Vladivostok. Across Russia, from Kaliningrad to Kamchatka, the spread is 10 hours. A single batch send cannot hit the right time for everyone.

Business type. A B2B software company and a clothing retailer land in completely different contexts. A procurement manager checks work email from 9 to 6. A parent with a newborn scrolls their phone at 11 pm once the baby is asleep. Tuesday morning is right for the first; Thursday evening or the weekend may be right for the second.

Inbox competition. When every marketer in your niche acts on the same “Tuesday, 10 am” advice, that slot becomes the week’s most competitive hour. Brevo records 8-14% higher open rates at less common times: early morning (6-7 am) or late evening (8-9 pm).

Email type. Transactional emails (order confirmations, password resets) get opened whenever they arrive; timing optimization does not apply. Promotional campaigns are highly time-sensitive. Digests and educational content sit in the middle: a subscriber might save them for later. Promos need an immediate reaction; content emails need to land when the person is ready to read.

Industry averages are a map. Useful, but you still have to find your own route.

Days of the week: a closer look

Monday. Inboxes are clogged from the weekend. Many subscribers process the backlog by mass-deleting anything that doesn’t look urgent. Open rates typically run 3-5% below the weekly average. That said, B2B campaigns with a strong offer can work on Monday: the recipient is in work mode and ready to act.

Tuesday. The classic favorite. The Monday backlog is cleared, the end of the week feels distant, attention is available. GetResponse puts Tuesday open rates 1-2 percentage points above the weekly average. But everyone knows this, so competition is highest.

Wednesday. Mid-week, close to Tuesday in performance. A solid alternative if you want to avoid the Tuesday rush while staying in the productive part of the week.

Thursday. The second-strongest day. For e-commerce it often beats Tuesday because people are starting to plan weekend purchases. Omnisend reports Thursday produces the highest revenue per email for online retailers.

Friday. Depends on the audience. B2B typically dips: people are closing out tasks, not reading newsletters. Entertainment, restaurants, and travel fare differently since the subscriber is already thinking about the weekend.

Saturday and Sunday. The weakest days on average, with clear exceptions: hobbies, sports, entertainment, food delivery. Klaviyo data shows that brands consistently sending Saturday mornings achieve open rates on par with Wednesday. The reason is simple: the inbox is emptier and competition is lower.

Time of day: what the numbers show

6:00-8:00 am. An early spike. People check their phones right after waking up. Open rates are high, and click rates are especially strong: if your email is first in the inbox, the chance of action is at its peak. Works well for daily digests and news newsletters.

9:00-11:00 am. The main work peak. Highest raw volume of opens. B2B campaigns perform best here. The catch: it is also peak competition for attention.

1:00-3:00 pm. Post-lunch window. People return to their desks and scan what arrived during the break. Less competitive than morning. Good for longer emails and educational content, since the subscriber has 10-15 quiet minutes.

5:00-7:00 pm. An underrated B2C slot. The workday is done, the subscriber is commuting or unwinding, and personal email gets attention. Omnisend records 5 pm as the click peak for e-commerce. Promotional emails with time-sensitive offers tend to do well here.

8:00-10:00 pm. Late evening. Mobile opens account for 80%+ of reads in this window. Works for entertainment content, subscription services, and media. For B2B it does not belong in the mix.

Send Time Optimization: automation over guesswork

Most modern ESPs offer Send Time Optimization (STO). The principle: the platform looks at each subscriber’s individual open history and delivers the email at the hour when that person typically reads their inbox. Not 10 am for everyone, but 8:30 for one subscriber, 1:15 for another, 7:00 pm for a third.

Brevo reports STO lifts open rates 5-12% on average; HubSpot says 8%; Mailchimp puts it at 4-7%. The spread reflects algorithm differences, but the direction is consistent: personalized timing outperforms a fixed send time.

One limitation: for new subscribers with no open history, STO uses segment averages. Accuracy improves after 3-5 campaigns. If your list turns over fast (30%+ new subscribers per month), the uplift will be modest.

How to run your own time test

Others’ data gives you a starting point. Your own data gives you an answer. Here is a concrete plan that takes 3-4 weeks to run.

Step 1. Test one variable. Start with day of week, keeping the time fixed. Then test time of day with the day fixed. Changing both at once makes it impossible to know which factor drove the result.

Step 2. Split the list into equal groups. Two groups minimum, four or five for more precision. Randomize the split; do not divide by signup date or region, or you measure segment differences rather than timing differences.

Step 3. Send the identical email. Same subject, preheader, content, sender. Sending group A a shoe promo on Tuesday and group B a jacket promo on Thursday tests offers, not timing.

Step 4. Wait 48 hours. A large share of opens occur in the first two days. Measure 48 hours after each send for a fair comparison.

Step 5. Repeat 3-4 times. One test is an anecdote. A result that holds over 3-4 consecutive tests is data. If Tuesday consistently beats Thursday over a month, Tuesday is your day.

What matters more than send time

Send time genuinely affects open rate. Its contribution is roughly 5-15% of the total outcome. These factors have more leverage:

List quality. If 20% of your addresses are invalid, no send time rescues your open rate. Dead addresses drag down the metric and damage domain reputation. Our data shows lists lose 22-25% of addresses per year without regular cleaning. Validating your list before experimenting with timing is step one.

Subject line. The subject determines whether the email gets opened at all. The gap between a good and a weak subject line is 10-30 percentage points of open rate. The gap between good and optimal timing is 2-5 points. Work the subject line first.

Deliverability. An email in spam does not get opened at 10 am or 10 pm. SPF, DKIM, and DMARC need to be configured, your domain needs to be warmed, and bounce rate needs to stay in range. Optimizing timing without that foundation is like choosing wallpaper for a house without a roof.

Segmentation. A single blast to the full list always underperforms a segmented send. Active subscribers can get emails more often; dormant ones need less contact and only your best content. Segmentation lifts open rates 20-40%. Timing adjustments lift them 5-12%. The priorities are clear.

Quick recommendations by business type

• B2B, SaaS: Tuesday through Thursday, 9:00-11:00 am. Start with Tuesday at 10, then test Wednesday and Thursday.
• E-commerce: Thursday and Tuesday, 8:00 am or 5:00 pm. Thursday captures pre-weekend buying intent. Test evening sends.
• Media, content: Tuesday or Wednesday, 6:00-8:00 am. The early morning slot works well for digests.
• Education, online courses: Monday through Wednesday, 9:00-10:00 am or 7:00-8:00 pm. Learning content gets opened both in the morning and in the evening.
• Entertainment, restaurants, delivery: Thursday through Saturday, 11:00 am-1:00 pm or 5:00-7:00 pm. Closer to the moment people decide what to do.

These are starting points, not rules. Run tests and adjust based on your own results.

Checklist: where to start

• Check your list for invalid addresses. Remove dead mailboxes so your metrics reflect reality.
• Look at past campaign analytics: which day and hour had the highest open rate? That is your baseline.
• Run an A/B time test: two groups, one email, different send times. Repeat 3-4 times.
• If your ESP supports STO, turn it on. It typically adds 5-12% without manual effort.
• Review results quarterly. Subscriber behavior shifts with vacations, holidays, and seasonality.

There is no universally perfect send time. There is your send time, found through testing on your own audience, with a clean list and solid deliverability. Start from data, not other people’s advice.