SMS delivery rate is the share of sent messages that reach the handset, and latency is the time from submission to delivery. On good A2P routes, delivery rates are typically in the 90s (percent) and most messages arrive within a few seconds; both should be measured per country, per network and per route, and checked against real handset tests because delivery reports can be wrong.
How to calculate delivery rate
The basic formula is delivered messages divided by submitted messages, using the final DLR status. Decide up front how you treat each case:
- DELIVRD counts as delivered.
- UNDELIV, EXPIRED, REJECTD count as failed.
- No DLR or UNKNOWN should be reported separately, not hidden in either group.
- Rejected at submission (non-zero SMPP status) is a separate failure type. See common SMPP error codes.
Count long messages once, as delivered only when all parts are. Status meanings are in SMS DLR statuses explained.
What is a normal delivery rate?
There is no single number. A clean, opted-in list on a direct route often delivers 95% or more. Old marketing lists contain many inactive numbers, so the rate is lower even on perfect routes. Some countries and networks report delivery less reliably. Compare routes on the same traffic, not against a generic benchmark. A route reporting close to 100% everywhere, including on numbers you know are inactive, is more likely to be sending fake DLRs than to be perfect.
Measuring latency
There are three useful intervals:
| Interval | What it shows |
|---|---|
| submit_sm to submit_sm_resp | How fast the supplier accepts messages; rises with congestion |
| Submit to DLR | End-to-end time as reported by the route |
| Submit to arrival on a test handset | The real user experience, used to validate the DLR time |
Look at percentiles, not averages: the median, the 90th and the 95th percentile. An average of 4 seconds can hide 10% of messages arriving after a minute, which is a failure for OTP. See OTP SMS best practices.
Common causes of low delivery or high latency
- Invalid or inactive numbers: clean lists with format validation or an HLR lookup.
- Sender ID not registered where registration is required, leading to REJECTD. See sender ID registration.
- Content filtered by an operator firewall, often for links, keywords or URL shorteners. See SMS firewalls explained.
- Too many hops: indirect routes queue messages at each provider.
- Throttling: sending above your allowed TPS creates a backlog.
- Network or handset state: phones off, out of coverage or with full memory lead to EXPIRED after the validity period.
Monitoring in practice
- Build a dashboard per country, network (MCC/MNC) and supplier, updated at least hourly.
- Set alerts on relative changes: for example delivery rate down 5 points, or 95th percentile latency doubled, compared with the last 7 days.
- Run small automated handset tests daily on key destinations, as in how to test an SMS route.
- For OTP, add conversion rate: it catches problems DLRs miss.
- Keep a backup route ready per key country so you can move traffic within minutes.
Improving your numbers
Most improvements come from the route, not the sender's code. Moving critical traffic to direct routes usually lifts both delivery and speed. VoIPMatcher sources A2P SMS routes from its carriers and manages them for you. Request an SMS route with your current delivery and latency figures.
Frequently asked questions
What is SMS latency?
SMS latency is the time between submitting a message and its arrival on the handset. On good A2P routes most messages arrive within a few seconds. Measure it with percentiles rather than averages, because a small share of messages arriving after a minute ruins OTP flows even when the average looks fine.
Why are my SMS delayed?
Common causes are indirect routes that queue messages at each hop, sending above your allowed TPS, operator firewalls holding unregistered sender IDs, and phones that are off or out of coverage. Compare submit to DLR times per network and supplier: a delay on one network usually points to the route, not to your platform.
Do undelivered messages count in SMS cost?
On per submitted billing, yes: you pay for every message the supplier accepts, delivered or not. On per delivered billing you pay only for DELIVRD reports, which makes report accuracy important. Either way, compare offers by cost per delivered message, using the delivery rate measured with your own tests.
What is the difference between delivery rate and conversion rate?
Delivery rate is the share of messages the route reports as delivered. Conversion rate is the share of recipients who act on the message, such as entering an OTP code. For OTP traffic, conversion is the more reliable metric, because it catches problems that delivery reports miss, including fake DLRs and messages filtered on the handset.
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