What a duty cycle is
The Things Network defines duty cycle simply: the fraction of time a resource is busy. Its example is a device that transmits on a channel for 2 time units out of every 10, which gives a duty cycle of 20%.
The resource can be a channel, a whole device or a sub-band, and the numbers differ for each. If that device sends on 3 channels instead of one, each channel is still busy 20% of the time, but the device is transmitting 60% of the time. If two of those channels sit in the same sub-band, that sub-band is busy 40% of the time. Regulations say which of these the limit applies to, so it matters which one a device counts.
A duty cycle limit caps that fraction. It is one way of sharing spectrum that devices use without an individual licence: each transmitter gets a bounded share of airtime, whoever else is nearby.
The European 868 MHz example
The clearest worked example is Europe’s band around 868 MHz, used by LoRaWAN, Meshtastic and other short range devices. The harmonised standard ETSI EN 300 220-2 covers short range devices from 25 MHz to 1,000 MHz. Its clause 4.3.3 says the duty cycle at the operating frequency shall not exceed the values in its annex B, and that duty cycle applies to all transmitters except those using polite spectrum access, where that is permitted.
Annex B, table B.1, of version 3.2.1 sets these limits for the sub-bands between 863 and 870 MHz:
| Sub-band | Frequencies | Duty cycle limit | Maximum e.r.p. |
|---|---|---|---|
| K | 863 MHz to 865 MHz | 0.1% or polite spectrum access | 25 mW |
| L | 865 MHz to 868 MHz | 1% or polite spectrum access | 25 mW |
| M | 868.0 MHz to 868.6 MHz | 1% or polite spectrum access | 25 mW |
| N | 868.7 MHz to 869.2 MHz | 0.1% or polite spectrum access | 25 mW |
| P | 869.4 MHz to 869.65 MHz | 10% or polite spectrum access | 500 mW |
| Q | 869.7 MHz to 870 MHz | 1% or polite spectrum access | 25 mW |
Polite spectrum access, set out in clause 4.5, combines a clear channel assessment before transmitting with adaptive frequency agility, and replaces the time cap where the table allows it. The same table has another entry for 869.7 MHz to 870 MHz with no duty cycle requirement but a 5 mW limit and further usage restrictions, so check the full row for your use.
Alongside the standard sits CEPT’s ERC Recommendation 70-03 on short range devices, last amended on 5 June 2026, which records national implementation and national restrictions in its appendices. Check those before assuming a limit holds in a given country.
Not every region uses duty cycle
The United States regulates the 902 to 928 MHz band differently. Under 47 CFR 15.247, a frequency hopping system there whose hopping channel is narrower than 250 kHz must use at least 50 hopping frequencies, and its average time of occupancy on any one frequency must not exceed 0.4 seconds within a 20 second period. Systems using digital modulation instead must have a minimum 6 dB bandwidth of 500 kHz. These are limits on dwell time and bandwidth, not a percentage of airtime.
Meshtastic’s region table shows the effect in practice. It lists its United States region as 902.0 to 928.0 MHz with a 100% duty cycle, and its EU_868 region as 869.4 to 869.65 MHz with 10%, which is sub-band P above.
How devices stay within the limit
The Things Network’s advice starts with the arithmetic: work out how much airtime each message takes, then choose a transmit interval that keeps the total within the limit. Firmware and radio modules can also enforce it.
- Per channel. The Things Network notes that the RN2483 module enforces the limit per channel and reports
no_free_chonce it is reached. Splitting a sub-band’s limit evenly across its channels is easier to implement: its example is 8 channels in a 1% sub-band, giving each channel 0.125%. - Rolling window. Meshtastic applies the European limit as an hourly 10%, calculated every minute on a rolling one-hour basis. A device that reaches it stops transmitting until it is allowed again. Its
override_duty_cyclesetting turns this off, and the documentation warns that the device might then violate regulations. - Network policy on top. Operators can be stricter than the law. On The Things Network’s Sandbox, a fair use policy limits each node to 30 seconds of uplink airtime and 10 downlink messages per day.
What it means for design
A duty cycle limit turns airtime into a budget, and every design decision spends it. Meshtastic’s presets show the trade: its longest-range preset has the highest airtime and its fastest the lowest, so longer-range settings use the budget faster. Acknowledgments, retries and downlinks all count, and The Things Network stresses that gateways must comply too.
Meshes feel the budget in a particular way. In flooding, every node that rebroadcasts a message spends its own airtime budget on someone else’s traffic, so relaying competes with each node’s own messages. Designs that send small payloads, batch readings, cap hop counts and queue messages for later live within the limit more easily than ones that assume the radio is always free. The band itself, and who else shares it, is covered in what are the ISM bands.