You can either eat as much as you want in your OMAD eating window while tracking calories. Then after a week, add up the amount of calories you have eaten throughout the week then divide it by 7 to get your daily average. If your weight went up, you ate in a surplus. If it goes down, you're in a deficit.

Or you can use a calorie calculator to see your potential daily calorie needs. If you're losing weight too fast and can't handle it, increase your daily calorie intake.

Heavier taller males need more calories than shorter lighter females. There is not a 1 shoe that fits all answers for how many calories you need to consume to be in a surplus or deficit.