Oppinions- is my work day a workout?!

I think whether or not you eat more on those days is relative.

Like, what is your height, weight and current calorie goal without exercise added? If you're using a Fitbit or some tracking device, I'm not clear as to why you don't trust it?

I would eat more, probably more like 300-500 calories more, but I've tracked food and activity for 15 years so I'm pretty confident about my intake and output. Your own personal data over time should be your guide. Track it and adjust over a month's time.

That averages out to losing over 3 pounds a week. Not sure what your goal weight is, but no reason to be set at 1200 with those statistics. Two pounds a week is considered aggressive. You could probably stand to add some of those calories back. Not 800 calories as the 800 would include your regular activity plus the extra. I'd probably go with around 250-300 extra on those days.

There are 2 ways to handle it on MFP. You can up your activity level to coincide with your average step count of 7000 (lightly active) and eat all calories allotted, or you can stay at sedentary (abased on 3000-4000 steps) and add your high step days as exercise.

For me eating too little for too long just leads to binging eventually.

Good luck!

It doesn't really matter whether you count it as exercise/workout, or factor it into your daily life activity level since it's your job. That's semantics and accounting. What's for sure is that you should account for it somehow.

If you're losing 3 pounds per week (or thereabouts), you've been eating roughly 1500 fewer calories daily than you've been burning daily, on average over the time period. At 170 pounds, that's (IMO) scary fast.

A 5-week period is long enough to have a reasonable average. Use that information to adjust. (Note: The "standard calories" from MFP or other calculators are essentially just a population average for people similar to you. You're an individual. We always recommend that people adjust calories based on average real-life results after 4-6 weeks; ideally for women, comparing weight at the same relative point in at least two different menstrual cycles.)

Like kshama and others said, don't lose that fast, it's not a good plan at your current weight.

What's a good plan? Losing 0.5-1% of your current weight per week, with a bias toward the lower end of that range unless you have an acute health problem that's created or worsened by your weight. (If you do have such a health problem, and there must lose weight riskily fast, you should be under close medical supervision for deficiencies or health complications). So, at 170 pounds, a pound a week (500 calorie deficit) is probably good, for a while. The percent rule is pretty much in line with the chart above, for most cases.

What happens if you lose too fast? If you're lucky, nothing . . . but you're dramatically increasing risks of failure (because it'll feel harder as time goes by), and risks of health problems (ranging from fatigue/weakness at the easy end, to gallstones/sludge, muscle loss, suppressed immune system and worse at the extreme end).

Is it certain that bad things will happen? No. Just increased risk

It's really a risk management and risk tolerance question, but I'd advise you to eat more, and base your choice of how many more calories to eat on your eating logs and weight loss. Use the rough rule of thumb that 500 calories per day is a pound a week. That's not exact, but it's a decent approximation.

Best wishes.