I would like to know how this rule of khums applies :
1) Do we have to pay khums on left over food items in our house – for example- if the khums date is 30th April 2020 and I buy 10 kilos of rice on 1st april 2020 and I have 9 kilos left on 30th april 2020, do I have to pay khums on this 9 kilos? Does this apply to other things as well – example – left over biscuits, cooking oil, flour, etc.

2) Does this rule apply to non edible items – example if I buy shampoo on 1st april 2020 and I have used just a little till 30th april 2020, do I have to pay khums on this?

We were generally told that we have to wait 1 year before paying khums on anything but I have heard the above rule so I wanted to clarify

by

1- Yes, if these residuals could be sold.
2- If it could be sold, then yes, but normally nobody buys used bottle of shampoo or fragrance.
It depends on communities.

What you mentioned about the waiting for a year is applicable if you are not working.