Identify how you’re using marmalade: spreading (needs jam texture), baking (needs stable sweetness), or glazing (needs pourable thickness).
Match flavor first: aim for sweet + bright citrus + a hint of bitterness (pith) using zest, lemon, or a tiny salt pinch.
Measure using the substitute ratio; if the substitute is thinner than marmalade, simmer it briefly to reduce.
Taste and correct: add lemon juice for brightness, orange zest for aroma, or a pinch of salt to sharpen the citrus.
Rest 5 minutes (optional): this helps flavors meld, especially in glazes and baked fillings.