What does the Hardy-Weinberg equation predict?

Hardy Weinberg equation does not predict: it helps us to derive allele frequencies of a particular gene within a population.

equation could be applied to determine frequencies of different aleles (in percentage) within a population.

Homozygous recessive organisms are readily recognised in a population but organisms showing dominant phenotypic trait could be either homozygous or heterozygous. In other words, recessive alleles are carried within the genotype of heterozygous individuals though they exhibit dominant character.

Sum of frequencies of alleles of a gene is 1 according to HW equation. Also:

From the number of homozygous recessive organisms (represented by ##q^2##) in a population, allele frequency ( q ) of recessive allele is determined.

Hence 1-q is allele frequency (p) of dominant allele. Number of carriers (2pq) can also be derived.