As the comet orbits around the Sun, I gather that its tail loses mass due to solar wind and tidal waves. Approximately, from what distance (with respect to Sun) will the mass loss begin?
The mass loss begins at approximately 450-600 million kilometers from the sun. This begins roughly in an area between the end of the asteroid belt and 1 AU from Jupiters orbit.
Extract from wikipedia:
The coma is generally made of H 2O and dust, with water making up to 90% of the volatiles that outflow from the nucleus when the comet is within 3 to 4 astronomical units (450,000,000 to 600,000,000 km; 280,000,000 to 370,000,000 mi) of the Sun. Source