I lost 8 stone in a year, from 19 to 11. I averaged a stone a month for the first 6 months and about half a stone a month after that.
I did it by counting calories, no eating between meals, and gradually incorporating more exercise and movement. No special diets or weight watchers or slimming world.
I started by writing down every single thing I ate from breakfast to biscuits to secret chocolate stashes to tasting as I cooked. After that, I started cutting down on the sweet stuff then counting calories in everything I ate.
I maintain my weight by counting calories, walking and cycling. Have managed to keep it off for a few years now.
There may be a few people who say "but starvation mode!", there is no such thing as 'starvation mode' unless you are actually starving to death. It doesn't start after a couple of hours of no eating.
It is doable and it is easy to lose weight but the hard part is getting yourself in the right place. And remember, if you have a blow out one day and eat more calories than you need, just carry on with the new lifestyle you're beginning.