Question

When is your weight equal to mg ?

Answer 1

when acceleration is constant or zero.

Answer 2

Yes you are right but it is not always true.
Actually our weight is equal to the Normal force exerted by us on the surface of the contact .

1) Then when my weight is equal to the mg
= when I am in the rest about vertical motion means if I am not moving up or down .

For example ,
I am simply standing on the floor then there is no vertical motion hence
N = mg

2) Then when my weight is not equal to mg ?
= when vertical motion is happening .

For example :-
Consider we are moving up in The lift with acceleration " a "
Then
N - mg = ma
N = ma + mg

Here N is normal force exerted on floor by us so it our weight hence it is increase

If we are moving down with acceleration " a " then .
mg - ma = N
hence our mass reduces