The diastolic reading, or the bottom number, is the pressure in the arteries when the heart rests between beats. This is the time when the heart fills with blood and gets oxygen.
A normal diastolic blood pressure is lower than 80. But even if your diastolic number is lower than 80, you can have elevated blood pressure if the systolic reading is 120-129.
80-89 is stage 1 hypertension.
90 or more is stage 2 hypertension.
120 or more is a hypertensive crisis.