Q:

How many calories does the human body naturally burn per day?

Our body is constantly building, repairing and regulating cells, whether we exercise or not.
So our bodies are taking care of itself.
I'm a male, 5'6 tall and I weigh 74 KGs,
I have a desk job, but I exercise 2-3 times a week(light running, push-ups and basic dum bell workout).
I want to know approximately, how many Calories does the human body naturally burn per day?,
just for maintenance and keeping us alive?
Eg. If the body burns 1500 calories a day irrespective of what I do -
100(breakfast) + 500(lunch) + 400(dinner) - 1500(default) - 200(light exercise) 
= -700 ie. calorie deficit 
I want to be in a calorie deficit, 
so I can plan how much calorie intake should I take and yet rely on the body to at least not get me fat, even if I happen to skip a workout

A:

Calculate your Basal metabolic rate (BMR).

Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest.

What a BMR calculator does not include:

amount of physical activity
thermic effect of food
amount of lean muscle tissue
genetic predisposition – your metabolic rate may be partly decided by your genes
environmental temperature – if the temperature is very low or very high, the body has to work harder to maintain its normal body temperature, which increases the BMR
infection or illness – BMR increases because the body has to work harder to build new tissues and to create an immune response
dietary deficiencies – for example, a diet low in iodine reduces thyroid function and slows the metabolism.
hormonal and nervous controls – BMR is controlled by the nervous and hormonal systems. Hormonal imbalances can influence how quickly or slowly the body burns kilojoules

You should consider these things 

Then add how many calories you burn doing basic activities. There are many ways to do this. For example, multiply BMR with

1.2 points for a person who does little to no exercise
1.37 points for a slightly active person who does light exercise 1–3 days a week
1.55 points for a moderately active person who performs moderate exercise 3–5 days a week
1.725 points for a very active person who exercises hard 6–7 days a week
1.9 points for an extra active person who either has a physically demanding job or has a particularly challenging exercise routine

Or try more calculators and make an average. For example this calculator.
If you want to be very accurate, according to the number of hours of each activity try this calculator.
Also, consider a thermic effect of food.

Thermic effect of food (TEF) is the amount of energy expenditure above
  the basal metabolic rate due to the cost of processing food for use
  and storage.

