I am a novice excel user and cannot figure out a formula to use to stop a lot of manual copy and pasting.

In one worksheet I have all the information regarding mileage for a year. In column A I have all the dates and in column K I have all the mileage amounts. I want to create a formula which gives the total mileage per month in a single cell on another sheet. Is there a formula that counts up all mileage entries for a certain month? Now I have to just =SUM and select the relevant cells, and I have to change it every time I add a line.

Is this possible within excel using formulae and if so how do I create this formula. I have searched through excels help files and nothing seems to be able solve this problem.

Thanks in advance for any help or advice you can offer.