If you have 18.5, you suffer under weight.

Between 18.5 and 24.9, it is verry good.

Between 25 and 29.9, you suffer over weight.
It's not so bad, but you may not recover weight.

Between 30 and 39.9, You suffer over weight.
You should lose some weight (between the 5 and 10 kilo).
You make chance of certain diseases like: heart disease or diabetes

Above 40, your health is in danger.