Cardio & Calorie question...

For cardio, I think the recommended minimum is 30 minutes x 5 days a week for heart health. Beyond that, its up to you. Of course a body-building guru is against cardio.

I use a Fitbit One - LOVE it - and MFP. I log all food, water in MFP. I have a set a total daily burn goal (and increase every now and then) and make sure I move enough between regular activity & Cardio that Fitbit shows me hitting this #. It incorporates my BMR, which is roughly 1 calorie per minute, so if I'm within 180 calories of my burn goal by 9pm, I know I'll hit my target.

I explained that, to explain this: my current total burn goal is 2150 per day. I typically eat between 1400-1600 which gives me a 500 calorie deficit and a little extra to spare. Which I like, as I know Fitbit may be 'off' in my total burn estimation. And though I try not to, I may make errors in my calories in. So I like having this cushion.

As you get smaller, and fitter: your body will naturally burn less calories doing the same activity. You can increase intensity, or fit in more activity to make it up. And in time as you get closer to your goal - you'll probably need to drop your deficit. I plan to go to a 250/day deficit starting in August.

I explained that, to explain this: my current total burn goal is 2150 per day. I typically eat between 1400-1600 which gives me a 500 calorie deficit and a little extra to spare. Which I like, as I know Fitbit may be 'off' in my total burn estimation. And though I try not to, I may make errors in my calories in. So I like having this cushion.

Wait - you have a negative net calories every day?!

I think she means TDEE.

Thank goodness! Was really worried there for a sec!

My trainer ( an ex-body builder/weightlifter guy) told me yesterday that i should only be doing 1/2 hour of cardio a max amount of 5 times a week.

Depends on your goals. My main goal is a 125 mile cycle so that wouldn't match my goals. If he states that same "maximum" to everyone he isn't much of a trainer! Training needs to be put in context of goals, capabilities and restrictions.

My daily goal is 1340 and I'm more than satisfied at that goal but I worry that it is too low as I get lower in pounds

The goal is 1340 plus exercise calories. I would worry that if your loss stalls you won't have much wiggle room.

Do you eat back your cardio calories?

You bet. Much easier to estimate calories burned through cardio than strength training. IMO it's better to start with a cautious calorie deficit to make adherence easier for the long run and make adjustments based on results rather than calculators.

Do you have your loss set at 2lbs/week? I was losing 1-1.5 lbs per week at 1900-2000 (net) when I weighed 220 lbs.

You could probably eat more and ensure you don't lose as much muscle if you aimed for a slower weight loss.

My trainer ( an ex-body builder/weightlifter guy)

But does he know anything about fitness, is he a certified trainer?
Here's where you can search for people in your area who are certified by the American College of Sports Medicine:
http://members.acsm.org/source/custom/Online_locator/OnlineLocator.cfm

told me yesterday that i should only be doing 1/2 hour of cardio a max amount of 5 times a week.

That's the recommended *_minimum_* amount for everyone, and would be for _maintaining_ weight.
If you want to lose, you might have to do twice that.

Have a look at the "exercise" post on my blog.
http://www.myfitnesspal.com/blog/MKEgal

From the CDC (http://www.cdc.gov/healthyweight/physical_activity/index.html)
"To maintain your weight: work your way up to 150 minutes of moderate-intensity aerobic activity, 75 minutes of vigorous-intensity aerobic activity, or an equivalent mix of the two each week."
(The page explains moderate & vigorous.)

"Most weight loss occurs because of decreased caloric intake. However, evidence shows the only way to maintain weight loss is to be engaged in regular physical activity."

I'm 38 years old, 5'4" started out at 240.6 and in 6 weeks have lost 20 pounds (220 now).

Congrat's on the loss so far!
At 5'4", the top end of a healthy BMI range would be 140 pounds.
So you have 80 lb to go.

Again from the CDC:
"evidence shows that people who lose weight gradually and steadily (about 1-2 pounds per week) are more successful at keeping weight off ...
To lose weight, you must use up more calories than you take in. Since one pound equals 3,500 calories, you need to reduce your caloric intake by 500-1000 calories per day to lose about 1-2 pounds per week."
http://www.cdc.gov/healthyweight/losing_weight/index.html

So you should aim to hit your goal weight in no less than 40 weeks, up to 80.

I want to lose 100 pounds by next summer/ end of next year.

Sounds like you have a reasonable time frame already.

My daily goal is 1340 and I'm more than satisfied at that goal but I worry that it is too low

Go have a read of my post about setting goals.
1340 is within the acceptable range, you'd be losing a bit more than a pound a week.
Currently you need 2200 cal to maintain your weight at 220 lb.
To lose 1 lb a week, you should be at 1700 cal per day.
For 2 lb, 1200 cal (which is the lowest you should go without a doctor monitoring you).
Or you could eat 1400 calories (which would maintain you at 140 lb) and that will slowly but surely bring you to 140 lb.

as I get lower in pounds, will it make it more difficult to lose?

Yes, because your body will be using less energy to move around.
So you'll have to up the time, or the intensity, of your exercise, &/or reduce your calories.

Do you eat back your cardio calories?

If I hit my goal and am still hungry (rare) I'll have 1/3 to 1/2 of what I burnt off that day, definitely not all of it, because MFP tends to overestimate. And I don't make a habit of it.