I don't even know the correct way to phrase this title. Thank you in advance for your patience.

I have multiple bills that span different time frames, and I need come up with monthly amounts.

For example:

```
10/09/2018 - 12/11/2019 Water $ 77.58
11/15/2018 - 01/14/2019 Sewer $124.12
12/01/2018 - 01/31/2019 Trash $ 43.14
12/11/2018 - 02/14/2019 Water $ 68.99
02/01/2019 - 03/31/2019 Trash $ 43.14
```

They each span 2 months but with different start/stop points, and not at the beginning/end of the months.

I would like to enter the above into a table and then calculate how much Water + Sewer + Trash was for January, February, March, etc.

My first thought was to calculate the number of days covered by the period and then calculate the cost per day. But then I got stuck because I don't know how to go to the next step of *January's total is....*

I'm not sure of the correct way to approach this problem. I would appreciate any pointer tips, web page references, what do I actually call/categorize this problem as -- I don't even know the words.

Thank you.

N.B. part also.