I tried doing it with 3/4 formula bottle to 1/4 milk for a week, then we did half and half for a week and then 1/4 formula to 3/4 milk. Unfortunately at that point Matilda reacted badly to so much milk so she's back on formula and what we do is try it all over again every few months to see how she goes. Matilda reacts by having diarrhoea and a lighter coloured poo when she has too much cows milk at once. Good luck!