I thought of using this expression but (un)fortunately I did a quick check to find out that it is old-fashioned. I would like to know some current expressions that convey the same meaning. Below is the definition of the idiom under consideration.
(You) mark my words. (old-fashioned)
something that you say when you tell someone about something that you are certain will happen in the future That girl's going to cause trouble, you mark my words.
Best Answer
Mark my words, the phrase isn't all that outdated.
Nevertheless, I tried to think of other alternatives to this phrase, since that's what you asked for. I manage to think of a few:
Here are some excerpts where these phrases mean roughly the same thing as mark my words:
You can replace the bolded words with mark my words, and the passages will pretty much mean the same thing.
As for the currency of mark my words, an Ngram hints that its usage may have peaked about 100 years ago. Yet even in recent years it still dwarfs some of the alternatives I've mentioned:
I think the most interesting part of that Ngram, though, is the sudden spike in I guarantee it, which seems to coincide with Joe Namath's famous Super Bowl prediction, further discussed in this column.