Every so often
Definition 1 of 1
Pro Tip 1/3Frequency Varies
The exact frequency is vague—'every so often' implies different intervals for different activities or contexts. 
She cleans the attic every so often.
Pro Tip 2/3Non-scheduled
It implies no fixed schedule or plan—it happens when it happens. 
He checks the old email account every so often.
Pro Tip 3/3Informal Tone
Common in casual conversation, but less likely in formal writing. 
Every so often, we meet up for a casual game of soccer.