how to calculate hybridisation order? give formula with suitable examples

As we know metals are electropositive,they form ionic bond .When we talk about hybridisation we generally talk about the covalent bonding.
Ex-Consider the compound MN_Ywhere M is the central atom and N is the atom surrounding it.
Hybridisation of such compound is given by=y+1/2(group of element M-y*valency of element N )
the number thus obtained can be put in the formula of sp^1-3d^1-5
for example for the number obtained as 6.hybridisation sp^3d
for charged species such as MN_yK-
the hybridisation is given by =y+1/2(group of element M-y*valency of element N +k )
For positive charge put simply -k in the above formula in place of +k
I think with these formulas you can calculate the hybridisation of each and every compound
For ex-CH4
4+1/2(4-4) =4
So the hybridisation will be sp³