Decide your use case: dipping sauce (need bright tang), marinade (need balance that won’t taste harsh), or cooking/stir-fry (can tolerate a slightly sweeter swap).
Choose the closest option from the table: a soy + vinegar/lemon blend is usually the most ‘ponzu-like’ for flavor behavior.
Measure using the listed ratio, then taste and adjust: add a few drops more citrus/vinegar for brightness, or add a pinch of sugar for ponzu-style softness.
If your substitute is sweeter or thicker (like teriyaki), dilute with water first so it doesn’t turn glossy-sticky in hot dishes.
Use immediately for best brightness, or stir into warm food at the end to keep the citrus notes from fading.