You budgeted for an 80,000-contact flash-sale blast at "two cents a text." The invoice comes back at more than double. Nothing went wrong, you just budgeted the wrong unit. SMS bills by segment, not by message, and most promo copy is quietly two or three segments once you count the discount code, the link, and that one little 🔥 someone dropped into the subject line.
Full disclosure: I work for Ready, and we bill per segment with the carrier fee itemized separately, so this is exactly the kind of math our own customers get wrong before their first big send. Let me walk you through the two things that blow up a flash-sale budget, message length and the Growth-tier crossover, and give you a worksheet so your next one lands on number.
Segments, not messages, this is where the first doubling happens
A single SMS segment is 160 GSM-7 characters. Go one character over and the message splits into multipart segments of 153 characters each (the extra 7 bytes per part are reassembly headers). And the moment you include any emoji or special Unicode character, the whole message re-encodes and the per-segment limit drops to 70 characters (67 for multipart).
That last rule is the sneaky one. A flash-sale text that's a tidy 150 characters (one segment, two cents) becomes a three-segment message the instant you add a single emoji, because 150 characters at 67 chars/segment is three parts.
Here's a real-looking example:
🔥 FLASH SALE: 30% off everything for the next 4 hours only. Use code FLASH30 at checkout. Shop now → shop.yourbrand.com/sale Reply STOP to opt out.
That's about 148 characters with the emoji. Unicode encoding → 67 chars per segment → 3 segments. Strip the emoji and tighten the copy to 155 characters and you're at 1 segment. Same message, 3x the bill.
If you're deciding whether to send that promo as a longer SMS or switch to MMS, we worked the exact crossover in The Exact Message Length Where MMS Gets Cheaper Than Multi-Segment SMS.
Worked math: the same blast at one, two, and three segments
Ready's Standard rate is $0.02/segment plus a $0.0045 carrier pass-through, so $0.0245 all-in per segment. Hold volume at 80,000 contacts and watch what message length alone does:
| Message | Segments | All-in/contact | 80,000-contact blast |
|---|---|---|---|
| Tight copy, no emoji (155 chars) | 1 | $0.0245 | $1,960 |
| Longer copy, no emoji (~250 chars) | 2 | $0.0490 | $3,920 |
| Copy + emoji (~148 Unicode chars) | 3 | $0.0735 | $5,880 |
So the gap between a disciplined one-segment promo and a sloppy three-segment one on the same list is $1,960 vs $5,880. That's the first "double what you budgeted", and it happened before anyone talked about tiers.
The fix is boring and free: write to the segment boundary. Drop the emoji, use a short branded link instead of a long one (and don't use a public shortener, those get filtered by carriers), and keep your STOP language terse.
The Growth-tier crossover: your cost drops 20% mid-blast
Here's the part most people don't plan around. Ready's Growth tier, $0.016/segment, $0.0205 all-in, applies automatically once your account crosses 50,000 segments in a calendar month. You don't pick it, you don't call anyone. The rate just drops for every segment past the threshold.
For an 80,000-contact, two-segment blast, that's 160,000 segments, so you blow past 50,000 almost immediately and most of the send bills at the lower rate. But when in the month you send decides how much of it qualifies.
Two scenarios, same 160,000-segment blast:
Scenario A, it's your first send of the month. The first 50,000 segments bill at Standard, the remaining 110,000 at Growth:
- 50,000 × $0.0245 = $1,225
- 110,000 × $0.0205 = $2,255
- Total: $3,480
Scenario B, you've already sent 50,000+ segments this month on other campaigns. The entire blast bills at Growth:
- 160,000 × $0.0205 = $3,280
That's a $200 difference on one send, purely from where the blast falls in your monthly volume. If you run frequent flows plus occasional blasts, your automated sends are likely pushing you over 50k before the flash sale even fires, which is good, because it means your big blast prices at the lower tier. We dug into the same crossover from an agency rebilling angle in At 50,001 Segments Your Cost Drops 20%.
A flash-sale budgeting worksheet
Run these five numbers before you schedule anything:
- Contacts after scrub. Start from your consented list, then subtract opt-outs and anyone flagged by litigator/DNC scrubbing. A $0.005/contact scrub on 80,000 is $400, cheap insurance against TCPA exposure that runs $500 to $1,500 per text.
- Segments per message. Paste your final copy into a character counter. Confirm encoding (GSM-7 vs Unicode) and multiply out. Assume the worst case if anyone might add an emoji.
- Total segments. Contacts × segments/message.
- Tier split. Have you already sent 50,000+ segments this calendar month? If yes, price the whole blast at Growth. If no, price the first 50,000 at Standard and the rest at Growth.
- Carrier line item. The $0.0045 pass-through is billed separately and isn't marked up, include it so the invoice doesn't surprise you.
Worked all the way through for the realistic case, 80,000 contacts, two-segment copy, first send of the month:
- Scrub: 80,000 × $0.005 = $400
- Messaging: $3,480 (from Scenario A above)
- Budget line: ~$3,880
If your gut said "$1,600, it's two cents a text," you'd have been off by more than 2x. Not because anything was hidden, because the unit was wrong twice over.
Why segment-level transparency matters here
Plenty of providers quote you a rounded "per-message" number with the carrier fee baked in, which makes blasts feel predictable until message length or volume shifts and the math no longer reconciles. Ready separates the per-segment rate from the $0.0045 carrier pass-through on purpose: when you look at a flash-sale invoice, you can tie every dollar to a count. We broke down why that line item matters in The $0.0045 Carrier Pass-Through Your Reseller Bakes Into a Rounded Rate.
Honest caveat: on raw per-segment price alone, Ready isn't the cheapest thing on the market, a bare CPaaS API will undercut us. What the per-segment line buys you is the full platform (CRM, automations, unified inbox, no per-seat fees), self-serve 10DLC that approves in 1 to 3 days instead of weeks of manual onboarding, and the automatic Growth drop you don't have to negotiate. For a brand sending flash sales, "I can model this exactly and the discount kicks in on its own" is worth more than shaving a fraction of a cent.
The practical takeaway
Two numbers decide your flash-sale bill: how many segments each message is, and how much of your monthly volume falls past 50,000 segments. Message length is the bigger surprise for most brands, a stray emoji turns a one-segment promo into three, and it's the one you control for free by tightening copy. The tier crossover works in your favor if you plan your monthly send order so the big blast rides on top of your existing flow volume.
Before your next sale, run the five-step worksheet, drop your real copy into the cost calculator, and price both tier scenarios. If the number looks right on paper, it'll look right on the invoice, which is the whole point of billing by the segment.