Moisture Stress
Overwatering or underwatering are the main causes of yellow indoor plant leaves.1 Potted plants must be watered only when needed.
Normal Aging
No worries here. To encourage new growth and bushiness, cut the main stem if the plant gets lanky.
Cold Draft
Tropical plants often turn yellow and shed leaves in cold gusts. Unlike short episodes of extreme cold, which brown leaves or form pale, translucent patches between veins.
Lack of Light
Too little light causes lower leaves to yellow before falling. If this is your problem, look for a clue.
Nutrient Deficiency
Insufficient nutrition might also turn plant leaves yellow. A nitrogen deficit or too much calcium in hard water might cause this.
Viral Infection
A viral infection may cause blotchy, yellow areas on your plant's leaves.
Pests
Plants with dry air indoors may have pests. Aphids and spider mites may be slurping sap from your leaves and discoloring it yellow.