ROI = (Gain – Spend) / Spend Let’s say you pay £100 a month to your ESP. That’s £1,200 a year. And you also have a marketing agency handling your email campaigns at a rate of £800 per month. That amounts to £9,600 a year. Your total email marketing spend per year is £1,200 + £9,600 = £10,800 If a lead brings you back £100 and your campaign brings 350 leads per year, your total revenue would be £35,000. Your ROI will be: [(£35,000 – £10,800) / £10,800] x 100 = 224,07%