Question 1

Why is SMS OTP more expensive than it looks?

Accepted Answer

Because a single successful phone verification almost never costs a single SMS. The sticker price you see quoted — a fraction of a cent per message in cheap countries, several cents in expensive ones — is the cost of one delivered text, but in the real world a meaningful share of codes never arrive on the first try. Carrier filtering, roaming users, wrong or recycled numbers, and users who simply do not receive the message all trigger a resend, and many flows let the user tap resend two or three times before they give up. Each of those retries is another billable SMS on your invoice, so a verification that lists at one cent can easily cost you one and a half. On top of that sits the country problem: your blended cost per message depends entirely on where your users are, and the same OTP that costs a fraction of a cent to a US number can cost ten or twenty times more to some international destinations, which is exactly where fraudsters point their traffic. And then there is the tax nobody budgets for — SMS pumping fraud, where bots trigger huge volumes of verifications to premium-rate numbers to skim the carrier payout, inflating your traffic with sends that deliver zero real users. Add retries, country mix and fraud together and the true cost per verification is routinely thirty to a hundred percent above the raw per-message quote. This calculator makes all three visible instead of leaving them in the footnotes of your bill.

Question 2

What is SMS pumping fraud and how much does it cost?

Accepted Answer

SMS pumping — also called artificially inflated traffic or toll fraud — is when attackers abuse your public verification endpoint to trigger huge volumes of OTP messages to phone numbers they control on premium-rate ranges, then collect a share of the termination fees the carrier pays out. To your system it looks like a flood of signups or login attempts; to your bill it looks like a spike in SMS spend for users who never convert into anything. Because the fraudsters steer the traffic to the most expensive international destinations, the cost per fraudulent message is often far higher than your normal blended rate, so a pumping attack can multiply a verification bill many times over in a single weekend. The damage is not just the wasted spend — it is unbounded, because an unprotected send endpoint with no rate limiting, no CAPTCHA and no per-number or per-IP throttling will keep paying out until someone notices. The fraud uplift input on this calculator lets you model that: set it to the fraction of your traffic you believe is illegitimate and the tool shows both the inflated total and the exact dollars going to fraud each month. The defences are well known — rate limiting per number and per IP, geo-blocking ranges you do not serve, a CAPTCHA or app-attestation gate before the send, and monitoring for sudden spikes to unusual countries — and every point of fraud you remove drops straight to the bottom line, which is why quantifying it first is worth doing.

Question 3

Should I use raw SMS or a Verify API?

Accepted Answer

It depends almost entirely on your volume and your delivery pain, and this calculator is built to find the crossover for you. A raw SMS approach bills you per message: you send the code yourself, you pay for every attempt including retries, and you own the delivery logic, fraud filtering and channel fallback. It is the cheapest option per unit at scale, but only if your delivery is clean and your endpoint is well protected, because every retry and every fraudulent send lands directly on your per-message bill. A managed Verify API flips the model — you pay a flat fee per verification and the provider bundles the retries, the channel fallback to voice or other channels, and a layer of fraud protection into that single price. That flat fee is typically several cents, far more than one raw SMS, so at very high volume raw SMS usually wins on pure cost; but for lower volumes, messy international delivery, or teams that do not want to build and maintain fraud defences themselves, the Verify API can be cheaper once you count the retries and pumping losses it absorbs. The honest answer is that the two curves cross, and where they cross depends on your per-message price, your retry rate and how much fraud you are exposed to. Enter your numbers and the calculator prices both side by side, tells you which is cheaper at your volume, and shows how the answer shifts as your delivery quality and fraud exposure change.

Question 4

How do I bring verification cost down?

Accepted Answer

Start with the lever that also stops fraud: protect the send endpoint. Rate limiting per phone number and per IP, a CAPTCHA or device-attestation gate before any SMS is sent, and geo-blocking country ranges you have no real users in will cut pumping traffic sharply, and because fraud is often the single biggest hidden line item, removing it is usually the largest saving available. Next, attack the retry rate: improving deliverability with a reputable sender, a registered sender ID or short code, and sensible message content reduces carrier filtering, so fewer codes fail and fewer resends get triggered — every avoided retry is a whole SMS saved. Then consider the channel. For users who have your app installed, an in-app or push-based code costs nothing per verification and sidesteps SMS entirely; falling back to SMS only when push is unavailable can move the bulk of your traffic off the paid channel. Where SMS is unavoidable, route by country and let cheaper regions use raw SMS while expensive or high-fraud destinations go through a managed Verify flow that caps the damage. Finally, size the free-versus-paid trade honestly: for many apps the verification cost per user is small next to the value of the account, but for high-volume, low-value signups it can dominate, and that is exactly when the fraud and retry math on this calculator decides whether your onboarding is affordable. Model each lever here — drop the fraud uplift, lower the retry rate, switch to the Verify comparison — and watch the monthly cost and the cost per successful verification move before you ship the change.

SMS OTP / 2FA 検証コスト計算ツール

コストの内訳 – お金の使い道

電話認証の 3 つの隠れたコスト

この計算機の仕組み

よくある質問

SMS OTP が見た目よりも高価なのはなぜですか?

SMS 送り込み詐欺とは何ですか?

生の SMS または Verify API?

検証コストを下げるにはどうすればよいですか?