As per the rules you have to satisfy the EWS rules for the fiscal year you are applying for. If in the next year it increases then it will not be a problem as increase in salary or decrement in salary is subject to several socio-economic conditions. So this things can't be adjust linearly.

The eligibility for the EWS certificate are:

• The annual income of the family of candidate should not exceed 8lakh per annum.
• The family should not hold 5 or more than 5 acres of land.
• The family shouldn't have a residental area more than 1000 sq feet.

To know more about JEE Advanced visit the link below:

https://engineering.careers360.com/exams/jee-advanced

I hope this answer helps. All the very best for your future endeavors!