I did a bit of research several years ago and opinions seemed to be that Windows Defender is perfectly adequate as an antivirus tool so ditched Avast.
Mate has a 10 year old laptop which hadn't been working properly in several years so he brought it to the pub last weekend for me to have a look; Win 10 with AVG and Defender both switched on. We decided that AVG should be disabled which I found difficult to do so I uninstalled it (what are you doing Treadders?); it did seem to be quite system hungry and I don't suppose there is much memory installed. I recommended that he look for a replacement when he has a bit of spare cash but at least it is working now (or I hope it still is!) and he is receiving emails, etc!