Take all your non US accounts. Find out the highest balance that each of them reached at any point during the year. Write those numbers down and then add them up.
If the total is over $10,000 then you need to file an FBAR.
Is that correct? So... hypothetically, if I have the equivalent balance of $5,950 at HSBC and $50 at Lloyd's from January 1 to June 30, then on July 1, I close my HSBC account and move that balance to Lloyd's, then the highest balance I'd have had at HSBC for the year was $5950, and the highest balance I'd have at Lloyd's for the year was $6000, for an apparent total of $11,950. But at no time did I ever actually have more than $6000 to my name. Is that how it's done?
I have always thought it was the highest aggregate value on a day. So each day, you would add up the balances of all your foreign accounts, and if their combined value on any one day was $10,000+, then you trigger FBAR.
For me, this has historically been a non-issue, as the only time I have had to worry about it before now was when I transferred my US savings to the UK last year for our down payment on our house. But since I've been saving in the UK, generally, and then added a separate savings account for my visa, I will be triggering a FBAR filing again this year and probably every year going forward (yay! I'm a grown-up with grown-up money!). I need to know this!