i plan to invest $100 weekly for 5 years ($26,000 total) to average market entry.
Op I think you are getting yourself confused,
Weekly investment you said : $100
Total for a month investment: $100× 4weeks = $400
And I think your yearly should be : $400 × 12 months = $4,800
In your previous calculations it seems you had an error, just like you said investing $100 per week would indeed result to a yearly investment of $4,800 and not 26,000 so take corrections of that.
You are the one that is confused and you have to correct your calculation by going back to check how many weeks we have in a year. I believed you are eager to correct when you have not checked it very well.
Even though we have 4 weeks a month, you don't have to calculate it like that because even though we have 4 weeks in a month, there is always a remaining day out of every month except February.
Okay let's do the mathematics here;
4 weeks makes a month with exception of 2 to 3 days.
Only February has 28 days to complete a full month
365/366 days(leap years) makes a year. If you divide 365 days by 7 days it will be 52.
Which means 52 weeks make a year.
52 × $100 = $5,200 per year
Since he said he would be investing $100 for a period of 5 years.
$5,200 × 5 years = $26,000
This means he would be investing $26,000 for a period of 5 years at an interval of $100 per week.
This is a typical DCA strategy, buying Bitcoin at different price range which is highly rewarding if he's holding for a long period of time.