Inter president Massimo Moratti and his Real counterpart Florentino Perez met to thrash out details of the package that will free Mourinho to leave and join the nine-times European champions after a treble-winning season in Italy.
While Spanish and Italian media reported that Inter would receive eight million euros, a statement from the Italian champions said: "Real will eventually have to pay all the clause in the contract."
Mourinho led Inter to three trophies last season, culminating in their Champions League final victory over Bayern Munich at Real's Bernabeu Stadium.
"We are convinced that we need a fresh impulse and we are convinced that Jose Mourinho is the right person to take on the job," Perez said at the time.
The move for Mourinho marks a change in direction for Perez, who has preferred to invest money in the world's best players rather than high-profile coaches in the past.
"(We looked to Mourinho) for his prestige, for the personality he has, for his great ability to absorb the pressure and for the leadership Madrid needs," Perez's right-hand man Jorge Valdano said in a radio interview earlier on Friday.
"We lacked a strong man in a moment of transition like this."
Real tripped up in the big games last season, losing in the 'clasicos' against Barcelona and in the Champions League first knockout round against Olympique Lyon.
Mourinho, 47, has a reputation as a motivator, is a great tactician and is strong enough to ride out the inevitable ups and downs of managing a side under the local media's microscope.
Spanish media have already speculated that Real will move back into the transfer market, with Inter's Brazilian full-back Maicon and Benfica's Argentine winger Angel Di Maria among the names linked with the club.
