Flash Sale Email: How to Run a 48-Hour Sale

KEY TAKEAWAYS

Run a flash sale for a reason you can say out loud: a season, a moment, a thank-you. Not because sales are slow this week.
Plan on about four emails for 48 hours, and turn Smart Sending off for them so the reminders actually go out.
Leave out recent full-price buyers, and send to engaged segments instead of your whole list.
Subject lines should say what they get and when it ends. Clever loses.

When does a flash sale make sense?

A flash sale works when it's an event, not a habit. The question I'd ask first: can you explain to a customer why this sale is happening now?

Good reasons sound like this: - The time of year (end of season, the start of the holidays). - Timing for the brand (an anniversary, a milestone). - Why the customer deserves it (a thank-you to your best customers).

What I wouldn't do is let customers in on the business. "We have extra inventory" or "we need to hit a number" tells people your full price isn't the real price. Give them context instead.

Will flash sales train customers to wait for discounts?

They can, if they're frequent and predictable. This isn't just a hunch. A long-running study in the Journal of Marketing Research found "consumers become more price and promotion sensitive over time" as brands increased promotions. Wharton researchers studying strategic shoppers put it simply: "If a strategic consumer concludes the markdown will be big and available, they will wait."

So the fix isn't "never discount." It's: - Make them rare. A few planned events a year, on your calendar ahead of time. My email campaign calendar post covers how to lay out the year. - Make them short. 48 hours is enough to create urgency without becoming the new normal. - Make them make sense. A clear reason (see above) means people don't assume there's always another one coming.

For the bigger picture on when discounts help and when they hurt, read my email discount strategy post.

How many emails should I send for a 48-hour sale?

Klaviyo's own flash sale guide lays out a preview, a launch and a reminder, and for longer sales suggests up to two emails a day. For a 48-hour sale, I'd plan four:

Heads-up (the day before): tell your engaged list what's coming and when. Optional early access for VIPs goes here.
Launch (hour zero): the offer, the end time, one button.
Reminder (day two, morning): what's still available, and the time left.
Last call (about six hours before it ends): short. Time left in the subject line and the header.

Turn Smart Sending off for these

Klaviyo's Smart Sending is on by default for campaigns. For email, it skips anyone who got a message in the last 16 hours. That's great on a normal week. In a sale with two sends a day, it quietly drops people from your reminders.

I keep Smart Sending on for normal campaigns and turn it off for deadlines, launches and multi-send days. A flash sale is all three. The same goes for BFCM: I make sure it's off on heavy send days so nobody misses the reminder that matters.

Show the deadline in words, not just a timer

Klaviyo doesn't have a built-in countdown timer. You'd use a third-party tool and paste it into an HTML block. Klaviyo's help article warns timers may not display right in Apple Mail with Mail Privacy Protection, and older Outlook shows only the first frame. So write the end date, time and time zone in the email itself. A timer is a nice extra, not the message.

Who should get the flash sale emails?

Not everyone.

Send to engaged segments

The best sale in the world sent to people who stopped opening a year ago still lands badly, and it can hurt where your next email lands. A sports training tech brand I work with sent to an engaged segment of 7,145 people and earned $0.19 per person. The same brand's blast to 49,475 people earned $0.04. Smaller, warmer, more money per person.

Leave out people who just paid full price

Nobody likes buying something on Monday and seeing it 25% off on Wednesday. Klaviyo's help center shows how: build a segment of people who ordered in the last few days (3 is its example, adjust to taste) and add it as an exclusion on the campaign. If you schedule the send ahead of time, turn on the setting that picks recipients at send time, so someone who orders the night before still gets excluded.

Think about active subscribers the same way. If they're getting a subscription price already, a flash sale can make that price feel worse. A note thanking them, or a perk that isn't a deeper discount, usually fits better.

What should the subject line say?

What they get, and when it ends.

The most common Black Friday subject line mistake I see is being too crafty, and the same goes for any sale. People on your email list want to know what they'll get and where. Across 2,821 campaigns from 7 brands, news beat brand voice, and vague questions did worst. At one sports tech brand, subject lines of 20 characters or less got more than twice the clicks of 41 to 60 character lines.

Some that follow that rule: - 25% off everything, 48 hours only - Ends tonight: 25% off - Last call: sale ends at midnight

Not sure whether percent off or dollars off works better for your list? Test it. I'd run a 50/50 split over a weekend and judge it on revenue. Black Friday is a good time to gather that data. My Black Friday subject lines post has more on what wins in a busy inbox.

How do I set up the discount in Shopify?

Two practical options:

One shared code with an end date. In Shopify, you can set active dates, a total number of uses, and one use per customer. Shopify says the discount expires on the end date at the end time you set, in your store's time zone.
Unique codes from Klaviyo. Each code can be redeemed once, though Klaviyo notes the recipient can still share it. For campaigns, the codes are generated ahead of time, at least one per expected recipient.

Watch the time zones. Klaviyo sets coupon times in UTC, while Shopify uses your store's time zone. Line up the end time in your emails with the end time in Shopify, or you'll get angry replies at 11:58 PM.

What about a flash sale during BFCM?

Black Friday is Nov 27 and Cyber Monday is Nov 30 this year. BFCM emails typically get 2 to 5 times the results of regular campaigns. So if you're tempted to run a flash sale the week before, ask whether it'll pull sales forward from your biggest weekend.

My usual move: set offers as early as possible, build a full calendar that builds anticipation, and save the urgency for the event itself. The full plan is in my BFCM email strategy post.

What should I decide first?

Before you write a single email, decide three things:

The reason. One sentence you'd be comfortable saying to a customer.
The offer and the end time. Exact, matched in Shopify and in the emails.
Who's out. Recent full-price buyers, and anyone who's gone cold.

Then the emails almost write themselves.

FAQ

How long should a flash sale last?

I'd keep it to 48 hours. Long enough for people to see it, short enough that the deadline means something.

How many flash sale emails is too many?

For 48 hours, about four is plenty: heads-up, launch, reminder and last call. Send them to engaged segments, not your whole list.

Should I use a countdown timer?

It's optional. Klaviyo needs a third-party tool for it, and timers don't display everywhere. Always write the end date, time and time zone in the email itself.

How do I stop flash sales from training customers to wait?

Run them rarely, keep them short, and give each one a real reason. Predictable, constant discounts are what teach people to wait.

Should I exclude recent buyers from a flash sale?

Yes. Klaviyo lets you add a segment of recent purchasers as an exclusion so people who just paid full price don't feel burned.

WRITTEN BY Jack White

Founder of Bardown Digital, a Chicago-based Klaviyo email and retention agency for Shopify brands. He's worked with brands doing $500K to $100M a year, with $100M+ in email-attributed revenue across them.

Instagram @jackintheinbox LinkedIn

SOURCES

Flash sale email: run a 48-hour sale without training discount hunters