That's because you're talking about 13 monthly contributions of €100 while I was talking about 12 monthly contributions of €100. Enter €100, 13 months and 7% into the calculator that I used and you will get the same result (well €52.60).I worked out manually that 100 a month for 12 months @7% will give interest before DIRT of 52.50. This corresponds to amount given in regular saver calculator.