Is it normal for your ovulation date to shift every few cycles or so?

With my most recent cycle I ovulated on CD11 & this same thing happened about 4 months ago, but every other cycle between that time period was CD15 right on schedule, is that normal? It’s just frustrating a little because I feel like now I’ll have to begin OPK testing way earlier & it might be for nothing if it doesn’t happen early again.

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