It's difficult to be accurate. I eat less than some guys but more than others. If, in your example, you weighed 95-kilos and 3600kcals a day maintained that level. Then you dropped to 88-kilos at 3000kcals but saw the scale moving towards 87 or 86-kilos I'd get you to add 200 calories. If it kept going down, but slower, we add another 200 and so on. The same applies with you gaining weight and so on.
The key is to not go crazy or freak out. Here's an easy example. I sit at about 280lbs usually (about 127kg). Recently I saw I was 273lbs. I realized I was slacking a little (and I mean a little) with my food. I tightened it up a bit and 10 days later I was 276lbs (same scales, same time etc). I added a shake so no more than 400 calories a day. If I add another back to my usual level it'll be 280lb next week. And that's how easy it is. Same for you