When you are using the Steps tracker on Healthbit, if you do not enter your own 'calories burned' then we will estimate the calories burned by you.
We base this on a person aged 45 and weighing 70kg who will burn approximately 400kcal by walking 10,000 steps briskly (3-5mph).
Where we receive steps data from devices that you have connected to your account, we will approximate the calories burned using the method outlined above.
Source: NHS Choices