In physics, an Effective Half Life is “the time required for the amount of a radioactive element deposited in a living organism to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination.”

I’ve reckon you could apply the same principle to recovering from a cold. Take the peak of the cold: each day you will be 50 per cent better, known as the half life, until the cold “decays” - i.e. you are healthy.

I reckon the peak of my cold was yesterday morning. Today I feel a lot better, but not fully recovered. So working out how better I feel than yesterday, I can calculate the effective half life of the cold. To get back to a level of healthiness in this case is around 3 half lives, which means I’ll be better by Monday. If I’m going to do the Leicester Half on Sunday, I’d better hope my calculations are wrong.