First of all, you should take into consideration that generally there are two things on the basis of which a person’s retired military pay is computed, namely the length of military service and the percentage of disability.
But now I want to refer to the computation of the retired military pay on the basis of one’s length of service in the military force. In this context, there are military retirement calculators that determine the amount of the retired military pay. There a three calculators and each of them have a specific formula.
So, if you are retiring from the military based on the length of service you may elect to have your retired pay computed by either the Final Pay Military Retirement Calculator, the High-36 Retirement Calculator or the CSB/REDUX Retirement Calculator.
The logical question is which one suits you better? Well, you have to keep in mind that your choice regarding the military retirement calculator first of all will be determined by the date you actually started your military service.
Final Pay Military Retirement Calculator may be used in order to compute the retired military pay for those entering military service before September, 8, 1980. This military retirement calculator computes the retirement pay under the Final Pay retirement system.
Also this military retirement calculator gives you the possibility to create different tables and charts that would reflect your personal situation. The main elements used by this retirement system are the length of the military service, retirement grade and age. However, this military retirement calculator takes into account for example the inflation rate.
High-36 Military Retirement Calculator may be used in order to compute the retired military pay for those who 
entered service between September 8, 1980 and July 31, 1986.
The High-36 Month Average retirement system is the system which belongs to this military retirement calculator. As the first military retirement calculator this one also gives you the possibility to draw up some tables and charts that would reflect your own situation. The elements included into the system represent the length of service, age and the retirement grade. And it also takes into consideration the economic changes such as for example inflation.
And finally, CSB/REDUX Calculator may be used in order to compute the retired military pay only for members who entered military service after July 31, 1986.
The CSB/REDUX retirement system represents the system through which your military retired pay is determined. This military retirement calculator is for those persons who have elected CSB/REDUX.
As the previous two this calculator gives you the possibility to create charts and tables that would reflect your personal situation. The elements of this system comprise except the length of service, age and the retirement grade also the value of the CSB (Career Status Bonus), which represents $ 30,000. The economic changes are taken into account as well.
Actually, if you are still confused you can do a little bit more research on the comparison of these three military retirement calculators.