How does Vanguard calculate "Personal Performance"?

[MustacheAndaHalf]

Rather than reveal my account value, let's say it holds $10,000 and I'll divide all the actual amounts by the same multiple.

I started with $4200 one year ago.
In March 2020, I added $580 near the market bottom.
So as of March 2020, I had $4780 in the account.

Vanguard's "account" menu has a "personal performance" option near the middle of the lists.  I selected "retirement account" only, and it shows a personal rate of return of 37%.

But my current balance shows as $10,000, or more than double the account value after adding money in March.  So I would expect 100% return or more, annualized.
$10,000 / $4780 = 2.09x, or a 109% return.

Any ideas on what Vanguard is doing for it's calculation?

[NotJen]

Their percentage only updates at the end of the month, so the current number shown is probably based on the value on Oct 31.

Otherwise, I’m not sure how they calculate it.

[MustacheAndaHalf]

I think that's the explanation, thanks!

When I ignore the timing of the added money, and divide the gains as of Oct 31st by the starting account value, I get 35%.  If I included the timing of purchases, I'd probably get 37%.