ESP8266 ADC maximum value is only 983...not 1023

My NODEMCU1.0(ESP12E) shows 983 instead of 1023 when i connect to 3.3 V pin( gives 3.3 V , confirmed from Multimeter), Why ? Everything else is fine.

The ESP8266's ADC can handle maximum voltage of 1.1v. The NodeMCU board has an on-board voltage divider for handling a 3.3v input. I'm quite sure the problem is the voltage divider. What's the actual voltage on the ADC pin on the ESP-12 module?