Worth knowing up front: once a Monstera leaf has gone fully yellow, it stays that way. Fixing the cause protects the rest of the plant, but the affected leaf is worth removing rather than waiting on.
Overwatering and root rot
The most common cause by a wide margin. Monstera likes consistent moisture, but soil that stays wet pushes air out from between the soil particles, and the roots suffocate and begin to rot without it. A plant with damaged roots can't move water up to the leaves properly even when the soil is soaked, which is what produces the yellowing.
The pattern here: leaves yellow as whole leaves rather than in spots, often starting low on the plant, and the stem may feel soft near the soil line. The soil itself frequently smells sour or swampy rather than earthy.
Fix: let the soil dry out fully before watering again — the top 2 to 3 inches should be dry to the touch. If you suspect it's gone further, slide the plant out of its pot; healthy roots are pale and firm, rotted ones are dark, mushy, and pull apart easily. Trim away anything rotted and repot into fresh, well-draining mix.
Bacterial leaf spot
This is the one people most often mistake for simple overwatering, because it's also caused by consistently wet conditions — but it isn't the same problem, and flushing the soil alone won't fix it. Bacteria that thrive in standing moisture infect the leaf tissue directly, usually where water has pooled on the leaf surface or collected in the natural splits of a mature leaf after overhead watering or misting.
The tell is the shape: small, water-soaked spots ringed with a distinct yellow halo, rather than a whole leaf yellowing evenly. Left alone, the spots enlarge and darken toward brown or black, and it can spread to neighboring leaves — or neighboring plants, if they're touching.
Fix: remove affected leaves with a clean, sterilized blade and isolate the plant from others nearby while it recovers. Improve air circulation around it, and switch to watering the soil directly rather than from overhead — wetting the leaves is what gives this one its opening. A copper-based bactericide can help in stubborn cases, but the watering change is what actually prevents it coming back.
Natural aging (not actually a problem)
A Monstera producing healthy new growth will often shed its oldest, lowest leaf occasionally as it redirects energy upward. The giveaway is that it's isolated — one leaf yellows fully while the rest of the plant, including any new growth, looks fine.
Fix: nothing needed. Remove the spent leaf if you want a tidier look, or leave it.
Underwatering
Less common than overwatering on this plant, but it shows up in bright, warm rooms or after a long gap between waterings. Leaves tend to yellow and turn crispy or curl at the same time, rather than staying soft, and the soil itself is dry rather than damp.
Fix: water thoroughly until it runs from the drainage holes, then return to checking the top few inches of soil by touch before watering again rather than following a fixed schedule.
Too little light
Monstera tolerates medium light reasonably well, but in genuinely dim spots new leaves can emerge pale, and older leaves may yellow gradually as the plant can't sustain as much foliage as it's carrying. This usually comes with longer gaps between leaves and stems visibly leaning or stretching toward the nearest light source.
Fix: move it to brighter, indirect light — a spot a few feet back from an east or south-facing window usually makes a visible difference within a few weeks.
Nutrient deficiency
Nitrogen is mobile within the plant, meaning it can be pulled from older leaves and redirected to new growth when the soil supply is low. That produces a fairly even yellowing across whole older leaves while new growth at the top stays green — distinct from bacterial leaf spot's ringed patches, and less isolated than the single-leaf pattern of natural aging.
Fix: resume feeding with a balanced liquid fertilizer at half strength during the growing season, but only once you've confirmed the roots are healthy — feeding a plant already dealing with root rot won't help and can make things worse.