You're not quite correct on the active duty retirement. There are two ways that service is calculated for retirement. There is "Service Creditable for Retirement Purposes" which determines when you are eligible for retirement. There is also "Service Creditable for Percentage Purposes" which determines the percentage of base pay that you will receive.
To be eligible to retire, you must have 20 years "Service Creditable for Retirement Purposes." Membership points, correspondence courses, UTA's, and any training under Title 32 orders are not creditable for retirement purposes. Any active service is creditable. This includes basic training, deployments, or any other time on Title 10 orders.
Once you reach 20 years and retire, your retirement pay will be determined by "Service Creditable for Percentage Purposes." At 20 years of creditable service, the multiplier for your retirement pay will be 50% plus 2.5% for every year after 20 up to 30 years (75%). If, at fifteen years of service, you elected to switch to the REDUX retirement plan (see #4
here), the multiplier will be 40% at 20 years plus 3.5% per additional year up to 30 years (75%).
You may then also add in your reserve time which was not creditable for service (membership points, UTA's, Title 32 orders) Full credit (number of days) is given for annual training or attending a military school under Title 32 orders. Additional credit is given at the rate of 1 point equals 1 day for UTA's and membership points (no credit is given for correspondence courses). For service after 30 OCT 07, you may count a maximum of 130 of these points per year. For service between 29 OCT 00 and 29 OCT 07, a maximum of 90 points per year may be counted. Between 23 SEP 96 and 29 OCT 00- 75 points and before 23 SEP 96- 60 points. The rate for these additional days is 1 year equals 2.5%. This is then added to the percentage calculated from your creditable service.
This and additional information may be found in the
DOD Financial Management Regulation.
Also, if you retire from the reserves, the age to receive retirement pay may be reduced below 60 years for an order to active duty under specific sections of Title 10 U.S.C. after 28 Jan 08. For each aggregate 90 days, the age would be reduced 3 months, but can be reduced no lower than 50 years.