Pay first bill in 1st week of month, wait for reward points which will be credited in 3-10 days. Repeat these till your cumulative spend reaches 40k. After getting points then you can do any number of transactions. Better pay all your dues on or before 20th so that you will get points in same month. If you make payment in last 3-4 days of month, then points may credit in next month and accelerated points calculations will start from zero.