diff --git a/src/LoRa.cpp b/src/LoRa.cpp
index 210a589..a8c459d 100644
--- a/src/LoRa.cpp
+++ b/src/LoRa.cpp
@@ -565,7 +565,7 @@ void LoRaClass::setCodingRate4(int denominator)
   } else if (denominator > 8) {
     denominator = 8;
   }
-
+  _coderate = denominator; // save coderate
   int cr = denominator - 4;
 
   writeRegister(REG_MODEM_CONFIG_1, (readRegister(REG_MODEM_CONFIG_1) & 0xf1) | (cr << 1));
@@ -751,4 +751,32 @@ ISR_PREFIX void LoRaClass::onDio0Rise()
   LoRa.handleDio0Rise();
 }
 
+double LoRaClass::Airtime_Message()
+{
+  int SF = getSpreadingFactor();
+  int BW = getSignalBandwidth();
+  int H = _implicitHeaderMode; // save header mode 
+  int PL = readRegister(REG_PAYLOAD_LENGTH);
+  int DE = 0;
+  if (((BW == 125E3) && ((SF == 11) || (SF == 12))) ||
+      ((BW == 250E3) && (SF == 12)))
+  {
+    DE = 1;
+  }
+  else
+  {
+    DE = 0;
+  }
+
+  int CR = (readRegister(REG_MODEM_CONFIG_1) & 0xf1) + 4;
+
+  double Tsym = pow(2, SF) / (BW)*1000;
+  double Tpreamble = (8 + 4.25) * Tsym;
+  int PrePay = ceil((8.0 * PL - 4.0 * SF + 28 + 16 - 20 * (1 - H)) / (4.0 * (SF - 2.0 * DE))) * (CR);
+  int payloadSymbNb = 8 + _max(PrePay, 0);
+  double Tpayload = payloadSymbNb * Tsym;
+  double Tpacket = Tpreamble + Tpayload;
+  return Tpacket;
+}
+
 LoRaClass LoRa;
diff --git a/src/LoRa.h b/src/LoRa.h
index b312db5..258e778 100644
--- a/src/LoRa.h
+++ b/src/LoRa.h
@@ -93,7 +93,7 @@ class LoRaClass : public Stream {
   void setSPIFrequency(uint32_t frequency);
 
   void dumpRegisters(Stream& out);
-
+  double Airtime_Message();
 private:
   void explicitHeaderMode();
   void implicitHeaderMode();
@@ -123,6 +123,7 @@ class LoRaClass : public Stream {
   int _implicitHeaderMode;
   void (*_onReceive)(int);
   void (*_onTxDone)();
+  int _coderate;
 };
 
 extern LoRaClass LoRa;