Calculate monthly sum

Hi all. This might sound like an amateur question. I have a very long data record of how much I get paid for business purposes and I record them on a daily basis with reference to the date. I want to know if there's a formula for me to sum up the income monthly. For now, I manually select the income from the beginning of each month until the end of the month to sum them up but I think it would be easier if there's a formula for it. I'll attach the file here as well for your reference. Thanks in advance.