Hii aspirant
Hope you are doing well amid covid-19 pandemic
As you've mentioned that your Crl rank is 45000
Crl rank is  defined as all India Rank prepared by CBSE for JEE mains it stands for common lost rank as per your CRL rank admissions are provided to General category students
Now the reservation process is like

• 7.5 % for ST
• 15% For SC
• 27% for OBC

So generally there is no algorithm that can predict your rank accurately but just by doing simple mathematics we can get your OBC rank relative to your CRL rank
As for OBC 27% reservation is there, so we will get 27% fro CRL rank and predict your OBC rank to be close to it
27/100*45000=12150
Now we wil do +- 400 to this rank so as to generate a lower and upper limit for your actual rank
Hope this helps
And if you want to know your predicted rank you can check it through the following link

https://engineering.careers360.com/jee-main-rank-predictor
Hope it helps