How do I work out my Economy 7 percentage? MSE Dan Updated June 28, 2017 16:29 Divide your night units by your total units (day and night), then times by 100, to work out your Economy 7 percentage. Related articles My tariff isn’t listed on Cheap Energy Club, what should I do? My existing supplier has offered me a cheaper deal. Should I stick with it? How do I find my MPAN/MPRN?