# Acid-Base Titration, why does for a weak acid indicator, [HA] = [A-]

I know that the end-point is when exactly all of the H+ ions from an acid have neutralised the OH- ions of the base.

The book later says

At the end point of a titration, the indicator contains equal concentrations of HA and A- and the colour will be inbetween the two extreme colours e.g. for methyl orange, the colour at its end point is orange.

It continues to say

For an indicator HA ⇌ $H^+$ + $A^-$
At the end-point, [HA] = [$A^-$] and $$K_a = \frac{[H^+][A^-]}{[HA]} = [H^+]$$

I am confused why this is true. why is the expression [HA] = [$A^-$] valid?

When an end-point is reached, the colour of the indicator will change with respect to the [$H^+$] concentration of the solution it is measuring.
As [$H^+$] increases, there will be a point when [HA] = [$A^-$] and depending on the indicator used by the person doing the titration, this would be close to the calculated equivalence-point.