Development teams argue about channels the wrong way. Someone reads that text messages get "90% open rates" and wants to move the whole appeal to SMS. Someone else points out that email is basically free and wants to leave everything where it is. Both are half right, and the argument never resolves because nobody puts the actual numbers next to each other.
Full disclosure: I work for ReadySMS, so I have a horse in this race. But the point of this post isn't to tell you SMS wins — it's to show you the math so you can tell where it wins and where email still beats it. For a lot of your calendar, email is the correct answer. For a few specific moments, it isn't even close.
Let's build the cost-per-dollar-raised model and run both channels through it.
The metric that actually matters: cost per dollar raised
Open rates and response rates are inputs, not outcomes. The number your board cares about is: for every dollar this appeal cost to send, how many dollars did it bring in?
Cost per dollar raised (CPDR) = total send cost ÷ total dollars raised.
Lower is better. A CPDR of $0.05 means you spent a nickel to raise a dollar. That framing lets you compare a nearly-free channel with mediocre response (email) against a channel that costs real money per send but converts far harder (SMS) — on the same scale.
To run it we need four things per channel: list size, cost per send, response/conversion rate, and average gift.
The assumptions (steal these, then swap in your own)
I'll use a mid-size nonprofit with a 25,000-person email list and a 6,000-person opted-in SMS list. The SMS list is smaller on purpose — it should be. It's people who explicitly said "text me," and it took real work to build. (If you're wondering whether double opt-in is worth shrinking that list further, we ran that math separately.)
Rough industry-approximate rates, framed as approximations, not gospel:
- Email: ~25–35% open, ~1–3% click, and for a fundraising appeal maybe 0.1–0.5% of the list actually donates. I'll use 0.3%.
- SMS: opted-in lists routinely see response rates in the 10–30% range on a clear ask, with donation conversion on a well-targeted appeal landing around 2–4%. I'll use 3%.
Average gift: I'll hold it at $50 for both so the channels are compared fairly, though SMS gifts often skew a bit smaller and more impulsive.
Cost per send: this is where the channels diverge
Email platform costs are usually a monthly subscription tied to list size — call it $150–$400/mo for a 25,000-contact list on a typical nonprofit-priced ESP. Per send, that's effectively fractions of a cent, and if you send several campaigns a month it drops toward zero. Email's marginal cost per additional send is close to nothing. That's its superpower.
SMS is priced per segment. On ReadySMS the published tiers are transparent, which is the whole reason this math is auditable:
| Tier | Monthly volume | Per segment | + carrier pass-through | All-in |
|---|---|---|---|---|
| Starter | 0–50,000 | $0.0155 | $0.0045 | $0.0200 |
| Growth | 50,000–500,000 | $0.0125 | $0.0045 | $0.0170 |
A 6,000-person SMS list sending a couple appeals a month sits in Starter, so $0.02 per segment all-in.
One thing that quietly doubles your SMS cost: emoji. A plain-text 155-character appeal is one segment. Add a 🙏 or an ❤️ and the whole message flips to unicode encoding, dropping the per-segment limit to 70 characters. A 155-char message with one emoji becomes 3 segments — $0.06 instead of $0.02 per recipient. Worth knowing before you decorate the ask.
The head-to-head: one appeal, both channels
Email appeal
- List: 25,000
- Send cost: ~$300/mo ÷ ~4 campaigns = ~$75 attributable
- Donors: 25,000 × 0.3% = 75
- Raised: 75 × $50 = $3,750
- CPDR: $75 ÷ $3,750 = $0.02
SMS appeal (assume a clean 1-segment, no-emoji message)
- List: 6,000
- Send cost: 6,000 × $0.02 = $120
- Donors: 6,000 × 3% = 180
- Raised: 180 × $50 = $9,000
- CPDR: $120 ÷ $9,000 = $0.013
On these numbers SMS both raises more total and costs less per dollar — mostly because the response rate gap (3% vs 0.3%) is enormous, and it swamps the higher send cost.
But that gap is doing all the work, and it isn't stable. It's widest on urgent, time-sensitive asks and narrows to nothing on routine communication. So let's stress-test it.
Where email actually wins
Run the same model on a non-urgent, informational send — a newsletter with a soft donate button, a program update, an event save-the-date. SMS response on that kind of message craters. People opted in for texts, not for a text-formatted newsletter, and a low-urgency ask might convert at 0.5% instead of 3%.
SMS, low-urgency:
- 6,000 × $0.02 = $120 cost
- 6,000 × 0.5% = 30 donors → $1,500
- CPDR: $0.08
Email, same content: it's basically free to send to a list this size, and low-urgency content is exactly what email readers tolerate. Even at 0.3% conversion, email's near-zero marginal cost keeps its CPDR around $0.02.
For everything routine — newsletters, most updates, long-form storytelling, receipts, the bulk of your calendar — email wins on cost and doesn't annoy anyone. Sending it by SMS is both more expensive and a faster way to earn STOP replies. (ReadySMS honors STOP automatically and propagates the opt-out across campaigns, but the best opt-out is the one you never provoke.)
Where SMS wins, decisively
SMS earns its per-segment cost in exactly the moments email can't reach:
- Deadline appeals. Year-end, matching-gift windows, "12 hours left." A message read in minutes beats one sitting unopened until Thursday. We wrote a whole year-end send schedule around this — roughly 30% of annual giving lands in the last three days of December, and that's a texting moment, not an emailing one.
- Recurring-gift upgrades. Converting one-time donors to monthly givers is a conversation, not a broadcast. A short 4-text upgrade flow can turn a $25 one-time donor into $300/year.
- Disaster / rapid-response. When the ask is genuinely urgent, the channel that gets read now raises the money.
- Two-way engagement. Reply-based asks and donor questions land in a conversations inbox — something email threads handle badly and SMS handles naturally.
The pattern: SMS wins when speed and response rate matter more than send cost, which is precisely when the 3%+ conversion holds up.
The costs the CPDR model hides
Two line items don't show up in the per-send math but belong in your real budget:
- 10DLC registration. To send bulk SMS on compliant carrier routes you register a brand (~$10/mo in carrier fees) and a campaign (~$20/mo). ReadySMS handles the registration in-app, approval typically 1–3 days. Unregistered traffic gets carrier-filtered, so this isn't optional — it's the cost of your messages actually arriving. We break down the nonprofit angle in The Impact of 10DLC on Nonprofit SMS Campaigns. Most nonprofits never need the optional $40 brand vetting upgrade; standard registration is plenty.
- Compliance risk. TCPA exposure runs $500–$1,500 per text on violations. Quiet-hours enforcement (holding sends outside permitted local hours) and litigator/DNC scrubbing at $0.005/contact are cheap insurance against an expensive mistake. None of it makes you lawsuit-proof — consent is ultimately your responsibility — but it's real risk reduction for pennies.
Spread across a 6,000-person program sending a few times a month, the ~$30/mo registration overhead adds a fraction of a cent to your effective per-send cost. It doesn't change the conclusion; it just belongs in the honest version of the budget.
The practical takeaway
Don't move your whole program to either channel. Split by urgency:
- Email carries the volume — newsletters, updates, storytelling, receipts, most soft asks. Near-zero marginal cost, no opt-out risk.
- SMS carries the urgency — deadlines, matching windows, recurring upgrades, rapid response. Higher per-send cost, dramatically higher response when the moment is right.
On my worked numbers, urgent SMS hit a $0.013 CPDR and low-urgency SMS hit $0.08 — a 6x swing driven entirely by whether the message deserved a text. Email stayed near $0.02 across the board. That's the whole decision in one sentence: use SMS when the timing is the point.
If you want to run these numbers with your own list size and average gift, the cost calculator does the per-segment math (emoji penalty included), and the pricing page shows exactly what a send costs — carrier fee itemized, nothing marked up. Start with 2,500 free credits and test one urgent appeal against your usual email version. Let the CPDR tell you which channel earned the moment.