At one time, there were also three GS supergrades (GS-16, GS-17 and GS-18); these were eliminated under the provisions of the Civil Service Reform Act of 1978 and replaced by the Senior Executive Service and the more recent Senior Level (non-supervisory) pay scale.
https://en.wikipedia.org/wiki/General_Schedule_(US_civil_service_pay_scale)
Each GS grade has 10 pay steps. Currently, a GS-9 starts at $41,979 for step 1 and reaches $54,570 per year at step 10 (not including locality pay adjustments). At the GS-9 grade, each pay step adds $1,399 to the annual salary. Pay steps are earned based on time in service and the employee’s work performance.
http://www.federaljobs.net/salarybase.htm
FORT GEORGE G. MEADE, Md. - Within-grade increases or step increases are periodic increases in a GS employee's rate of basic pay from one step of the grade of his or her position to the next higher step of that grade. Each General Schedule grade has 10 steps. * The employee's performance must be at an acceptable level of competence.
https://www.army.mil/article/60447/GS_grade_step_increases_made_simple/
The general schedule (GS) is the predominant pay scale within the United States civil service. The GS includes the majority of white collar personnel (professional, technical, administrative, and clerical) positions. As of September 2004, 71 percent of federal civilian employees were paid under the GS.
https://en.wikipedia.org/wiki/General_Schedule_(US_civil_service_pay_scale)
WITHIN GRADE INCREASE (WG/GS) Within-grade increases (WGIs), or step increases, are periodic increases in a General Schedule (GS) or Wage Grade (WG) employee’s rate of basic pay from one step of the grade of his or her position to the next higher step of that grade. The employee’s performance must be at an acceptable level of competence.
https://dmna.ny.gov/hro/tech/?page=1276788156
Fact Sheet: Within-Grade Increases. Description. Each General Schedule (GS) grade has 10 steps. Within-grade increases (WGIs) or step increases are periodic increases in a GS employee's rate of basic pay from one step of the grade of his or her position to the next higher step of that grade.
http://www.opm.gov/policy-data-oversight/pay-leave/pay-administration/fact-sheets/within-grade-increases
No doubt, OPM is aware of a recent report issued by the Federal Times that a miniscule number of federal employees are actually denied a within-grade increase (WIG). In fact, only one out of approximately every 1700 federal employees was denied a within-grade increase in 2009 or about .06%. And, despite the low percentage, that is actually a little higher than in previous years. In effect, a within-grade increase is automatic and based almost entirely on seniority.
https://www.fedsmith.com/2011/06/10/those-automatic-withingrade-increases-performance-based/
2017 Annual Rates by GS Paygrade and Step. The President announced an average civilian pay raise of 2.1% that will be split into a 1 percent across-the-board pay hike plus a 1.1 percent increase in locality pay. The actual raise civilians will see in their paychecks will vary depending on where they live.
http://www.federaljobs.net/salarybase.htm
As an example of the overall calculation, in 2016 a GS employee, Grade GS-12, Step 10 in Dallas would have received a base salary of $80,731 plus a locality pay adjustment of 21.04 percent (an additional $16,986) for a total salary of $97,717.
https://en.wikipedia.org/wiki/General_Schedule_(US_civil_service_pay_scale)
Those withholding a within-grade increase in most areas of the country will be holding back less than this example.) If this employee is promoted to a GS-12, step six, his salary will increase to $87,350—an increase of about $2,500 per year. When a within-grade increase is withheld, the employee can appeal.
https://www.fedsmith.com/2011/06/10/those-automatic-withingrade-increases-performance-based/
when are gs step increases
General Schedule step increases in a General Schedule employee's rate of basic pay from one step of the grade of his or her position to the next higher step of that grade.