Monthly Rate of return calculation for Bond portfolio

Can anyone tell me below mentioned way of calculating average rate of return for bond portfolio is correct or not? If any short coming here?

Avg balance of monthly Portfolio 12,811,089,655

Intrest income for the month 64,893,792

Average rate of intrest for the month 6.08%

Calculation steps:

=(64,893,792*360*100) / (12,811,089,655*30) = 6.08%

30 is number of days for the month

360-number of days for year

Simplifying my calculation,

Interet income for the month = 64,893,792

Daily interest income = 64,893,792/30

Therefore Annual Int Income = 64,893,792*360/30 = 778,725,504

Average rate of return for the portfolio is calculated as follows.

Annual Int income*100/ avg balance of portfolio for a month = 778,725,504*100/ 12,811,089,655

This equals 6.08% rate of return for the portfolio,

Appreciate very much for any feedback on this calculation.