Decide if you need classic ketchup for dipping/drizzling (thicker) or for cooking (slightly thinner).
Pick the closest option from the list: DIY tomato paste blend for tight ketchup match, sauce/reduced options for convenience.
Use the listed ratio, then adjust the balance: add sugar for extra sweetness and vinegar for sharper tang.
If your substitute is too thin, reduce 1–3 minutes on low or strain/briefly simmer to thicken.
Taste once—ketchup should be sweet-tart, not sour; tweak with more sugar or vinegar in tiny amounts.