How long does it take to change a habit? It varies, but one paper suggests it takes an average of 66 days. We ask writers to change one thing in their lives within that timeframe … and tell us if it works

I drink a lot of Pepsi Max. A slab of 30 cans has been known to disappear within a week. That’s upward of four 375ml cans a day – one and a half litres of sugar-free cola every 24 hours. Not enough to end up on My Strange Addiction but enough to concern friends. “Those things will kill you,” they tell me.

To be clear, there’s no evidence that Pepsi Max will kill anybody. Breathe easy, PepsiCo.