For those rare cases, it really isn't a problem to look at my work calendar on the work PC and my personal calendar on my phone and do a quick comparison.
In general, if I have a personal appointment, I'm not going to forget about it. Just the act of having added it to my calendar is enough to remember it, without having to look at the calendar. I only ever mix personal events into my work calendar if I there is an overlap with my working hours, everything else is none of my workplace's business, I'll polite decline any meeting that conflicts.
Besides, last-minute meetings are a sign of bad meeting culture.
In general, if I have a personal appointment, I'm not going to forget about it. Just the act of having added it to my calendar is enough to remember it, without having to look at the calendar. I only ever mix personal events into my work calendar if I there is an overlap with my working hours, everything else is none of my workplace's business, I'll polite decline any meeting that conflicts.
Besides, last-minute meetings are a sign of bad meeting culture.