Thinking about incorporating — how do director's loan accounts work?

A director's loan account is simply the running record of money moving between you and the company outside of salary and dividends — it can go either way, but the tax traps are all about when you owe the company money. You're right about both thresholds: if the loan is more than £10,000, it's treated as a benefit in kind, so the company pays Class 1 National Insurance on it and you report it on your Self Assessment. And if you don't repay within 9 months of the end of the company's accounting period, the company has to pay Corporation Tax at 33.75% on the outstanding amount — it's reclaimable once you repay, but HMRC keeps the interest. The cleanest approach is to keep the account in credit or clear any balance well before that 9-month point. Definitely one to keep a close eye on if you incorporate.