Spelling

There are couple of certain words that I cannot spell. I cannot spell them regardless of how many times I have written them in the past. I cannot spell them regardless of how many times I have read them in the past. I cannot spell them regardless of how many times I have checked the spelling in the past.

I simply 100% fail at the correct spelling each & every time I write them.

The worst one & the one which I come across the most often is "calender" (yes you can laugh). Even when I make a conscious effort to spell it correctly, knowing full well I get it wrong on a regular basis, I fail each & every time.

At best I might occasionally write "calander".

Is it just me or do you have the same problem? If so what word causes you the most issues?