My TDEE is 2050 calories.....

Since my TDEE is 2050 calories and I'm making a 20% cut, that puts my calories at 1640. That's how much I'm going to try to eat per day, but MFP suggests I eat only 1500 after I log my exercise. Do I still eat the 1640? And, do I eat 1640 on days I don't workout, or do I just eat like 1200 - 1400?

If you have figured out your own TDEE then you dont eat exercise calories as TDEE includes them and eat that everyday.
Did you select 2lbs a week weightloss goal from MFP? If so, I believe that may be why there is such a difference.

TDEE includes REGULAR daily activity. If you choose to include an estimated amount of exercise calories, then no you wouldn't need to factor exercise in, but most people don't calculate in exercise in their TDEE unless they are certain about the amount, type, and intensity (which is extremely difficult to estimate).

I would not recommend attempting to factor exercise into your activity level. That's going to be very inaccurate.

Your activity level, normally, should be based on your normal daily activity, I.E. work, before and after work activities (things you do around the house, daily chores...etc.). Exercise should ideally be calculated at the time of the activity.

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But when you pick your activity level on any TDEE calculator, it asks for how many days you exercise. o-o

STOP WORRYING ABOUT WHAT MFP SAYS. YOU AREN'T USING THEIR METHOD. STOP IT.

Since my TDEE is 2050 calories and I'm making a 20% cut, that puts my calories at 1640. That's how much I'm going to try to eat per day, but MFP suggests I eat only 1500 after I log my exercise. Do I still eat the 1640? And, do I eat 1640 on days I don't workout, or do I just eat like 1200 - 1400?

If you have figured out your own TDEE then you dont eat exercise calories as TDEE includes them and eat that everyday.
Did you select 2lbs a week weightloss goal from MFP? If so, I believe that may be why there is such a difference.

TDEE includes REGULAR daily activity. If you choose to include an estimated amount of exercise calories, then no you wouldn't need to factor exercise in, but most people don't calculate in exercise in their TDEE unless they are certain about the amount, type, and intensity (which is extremely difficult to estimate).

I would not recommend attempting to factor exercise into your activity level. That's going to be very inaccurate.

Your activity level, normally, should be based on your normal daily activity, I.E. work, before and after work activities (things you do around the house, daily chores...etc.). Exercise should ideally be calculated at the time of the activity.

]

But when you pick your activity level on any TDEE calculator, it asks for how many days you exercise. o-o

that's correct. Because when we exercise on a regular basis it raises our metabolic rate throughout the day, even if you skip a day of exercise, thus raising your average metabolic rate throughout the day whether or not you exercised that day. That doesn't mean you shouldn't still add exercise calories for that day.

I.E. someone who is considered active might have a metabolic rate of BMR multiplied by 1.5 to reach their normal daily metabolic rate as opposed to someone who is sedentary who's metabolic rate is BMR times 1.3 or so. Even if they don't exercise their rate is still calculated via the above formula's.

Now if they exercise that day, you're still adding the extra exercise calories to reach TDEE because MFP does not assume any exercise on a given day, which is why you put your exercise in the exercise log and add the calories.

MFP is all about keeping a consistant deficit based on what you can lose per week, not adding exercise calories causes the deficit to fluctuate, giving the body a less consistant amount of calories. This isn't the only method out there, but this method, if done correctly, allows you to have less fluctuation in your energy, meaning an easier way to lose weight as your body can "count" on a specific amount of energy.