There are actually 4 common causes of urinary incontinence. Some may experience incontinence for more than one of these reasons.
Physical exertion
Coughing, laughing, and in fact any type of exercise that involves the stomach muscles can cause urinary incontinence. This is more likely if your pelvic muscles have been affected by sugery or childbirth, or another medical condition.
Full bladder
If your bladder is full, you may experience the leakage of some urine. There are some medical conditions that prevent you from emptying your baldder effectively such as diabetes or prostate problems. Some medicines might also have this affect.
Restricted mobility
People with conditions that restricted their mobility might have perfectly normal control of their bladders, but not be able to get to the toilet in time to urinate because of their restrictions
Urge to urinate
Common in older people is the sudden urge to urinate, sometimes with not enough time to get to the toilet first. This might sometimes be a sign of a urinary tract infection. This type of incontinence can be addressed with bladder training and exercise.