Free tool

LoRaWAN airtime and battery life calculator

Enter spreading factor, bandwidth and payload size to get the time on air of a message, how many messages the 1 % duty cycle and The Things Network allow, and a rough battery life.

Result

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Transmit limits

Same payload at SF7–SF12 (125 kHz)

SF	Data rate	Time on air	1 %: max per hour	TTN: max per day

Battery life estimate

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Method and check

Time on air uses Semtech's LoRa modem formula (SX1276/77/78/79 data sheet, section 4.1.1.7; Semtech AN1200.13):

Tsym = 2^SF / BW
Tpreamble = (Npreamble + 4.25) · Tsym
Nsym = 8 + max(⌈(8·PL − 4·SF + 28 + 16·CRC − 20·IH) / (4·(SF − 2·DE))⌉ · (CR + 4), 0)
Time on air = Tpreamble + Nsym · Tsym

PL is the PHY payload in bytes. For a LoRaWAN uplink the CRC is on (1) and the header is explicit (IH = 0). Low data rate optimisation (DE) switches on automatically when the symbol time is 16 ms or more, which is SF11 and SF12 at 125 kHz. LoRaWAN adds 13 bytes to the application payload: MHDR 1, DevAddr 4, FCtrl 1, FCnt 2, FPort 1 and MIC 4 bytes (without FOpts).

Check: 8 bytes of application payload give 56.6 ms at SF7 / 125 kHz and 1,482.8 ms at SF12, the same values published in The Things Network community.

Example: at SF7 / 125 kHz (EU868 DR5), coding rate 4/5, an 8-symbol preamble and 10 bytes of application payload (23 bytes PHY), time on air is 61.7 ms. The 1 % duty cycle allows at most 583 messages per hour, and The Things Network fair use policy at most 486 messages per day. With 144 messages a day (one every 10 minutes), 45 mA transmit current, 10 µA sleep current and 80 % of a 2600 mAh battery, the estimate is 5,925 days (≈ 16.2 years). At such lengths self-discharge and shelf life decide battery life, and the calculator warns about it.

Limits: the 1 % duty cycle is a legal limit for the 868.0–868.6 MHz sub-band of ETSI EN 300 220. The 30 seconds per day is The Things Network's fair use rule, not a legal limit. The battery estimate leaves out receive windows, sensors and self-discharge.

Sources

Semtech, SX1276/77/78/79 data sheet, section 4.1.1.7 (Time on Air); Semtech AN1200.13, LoRa Modem Designer's Guide
LoRa Alliance, LoRaWAN 1.0.x Specification, MAC message format
LoRa Alliance, RP002-1.0.3 LoRaWAN Regional Parameters, EU863-870 data rates and maximum payload sizes
ETSI EN 300 220-2 V3.2.1, duty cycle of the 868.0–868.6 MHz sub-band
The Things Network, Fair Use Policy and EU868 frequency plan

Sources checked on 24 October 2026.

Using LoRaWAN in the field

What LoRaWAN is, how the network is built and where it pays off in industry is covered in our guide What is LoRaWAN. All calculators are on the tools page.

Frequently asked questions

Common questions

How is LoRaWAN airtime calculated?

With Semtech's LoRa formula. The symbol time is 2^SF / bandwidth. The preamble lasts (preamble + 4.25) symbols, and the number of payload symbols follows from packet length, SF, coding rate, CRC and header type. Time on air is the preamble time plus payload symbols × symbol time. LoRaWAN adds a 13-byte header and MIC to the application payload.

How long does a 10-byte message take?

In EU868 at SF7 / 125 kHz (DR5), coding rate 4/5 and an 8-symbol preamble, 10 bytes of application payload (23 bytes PHY) take 61.7 ms. The same message at SF12 / 125 kHz (DR0) takes 1,482.8 ms, about 24 times longer.

What does the 1 % duty cycle mean?

In Europe the default LoRaWAN channels (868.1, 868.3 and 868.5 MHz) lie in the 868.0–868.6 MHz sub-band of ETSI EN 300 220. In that sub-band a device may transmit at most 1 % of the time, or 36 seconds per hour. With a 10-byte message at SF7 that is 583 messages per hour.

Why is The Things Network limit tighter?

The Things Network fair use policy allows on average 30 seconds of uplink airtime per device per day and 10 downlink messages per day. With a 10-byte message that is 486 messages a day at SF7 but only 20 a day at SF12. A private network server has no such rule, but the legal 1 % limit still applies.

What is the largest payload at each data rate?

Per the LoRaWAN Regional Parameters (RP002-1.0.3) EU868 table, without FOpts the application payload is at most 51 bytes at DR0–DR2 (SF12–SF10), 115 bytes at DR3 (SF9) and 222 bytes at DR4–DR6 (SF8, SF7). The calculator shows an error above that limit.

How reliable is the battery estimate?

It is rough: it counts transmit and sleep current only. Receive windows, sensor readings, MCU wake-ups, self-discharge and temperature are not included. The default current and capacity values are examples; enter the values from your own device data sheet.