Reliably losing one pound a week (beyond the initial 1-2 week period where your weight is going to go all over the place due to water weight fluctuations) is as simple as cutting calories until you see the weight (on average, ignore fluctuations) drop by 1 lb a week. You have to average extensively. Bodies are very temperamental at this, unfortunately. My scale weight swings 0.5-1 lb quite frequently mainly due to sodium changes in my diet. It’s all about trend weight, though.