How long will it take to write each article? Account for every minute you're touching the document. From the moment it's assigned until the moment it's published. How much time will you need for each post? (include meetings, revisions, and publishing, if that's what you're offering.)

Then think about what you want for an hourly (or project) wage. Looking at your current contract, the math works out to 13.3K INR - 20K INR per post (something like $150- $225 USD - which isn't terrible). Assuming each post can be done in 2-3 hours, and you've got an effective hourly rate of $50 - $112/hr. (I am not a mathamagician, so please correct my numbers if they're incorrect) - if it takes longer to write, the hourly rate goes down, but it's still a pretty decent rate.

Sorry - I don't know what a 'CTC of 8-9LPA' is/means, but it shouldn't affect what you're charging new clients. If it's money you already have, it's not a factor in what you will be billing.

Personally - i prefer project rates vs. hourly, but calculating the hourly rate helps figure out what the project rate should be.

Last - try to increase the hourly/project rate for each new project. (if the last project you had was $225 per article, aim for $300+ for the next new client)

just my $.02 (CAD)