Out of baking powder? For about 1 tsp, mix 1/4 tsp baking soda with 1/2 tbsp vinegar or lemon juice and enough milk to make 1/2 cup; the acid reaction releases carbon dioxide

It's 9 pm on a Sunday, the oven has been preheated to 350°F, the batter is half-mixed, and that's when you pick up the baking powder tin only to discover it was empty, or or, worse, you grab the wrong white powder entirely, baking soda staring back at you instead of baking powder. This is the moment of dread you may have experienced when you've been in a period of pandemic banana-bread boom or the current "cozy baking" frenzy that has taken over our social media feeds. The good news is you don't have to run out to the grocery store to save the recipe. According to a Utah State University article, one option is to stir up a quarter teaspoon of baking soda into half a tablespoon of lemon juice or vinegar and then pour in some milk until you have half a cup. Crucially, that half-cup mixture isn't extra liquid poured on top of the recipe, it's meant to replace half a cup of the milk or other liquid the recipe already calls for. This is a simple trick that has worked in American households for decades without much thought.

Baking powder and baking soda are not the same

Part of what contributed to the panic setting in, when the right or wrong ingredient is in the cabinet, is that millennials may have been raised to believe these two ingredients are essentially interchangeable “rising powders.” However, they aren't interchangeable, and using them interchangeably is the source of all those flat, dense, or weirdly metallic-tasting home bakes. Baking soda is 100% sodium bicarbonate, which is a base. It does not affect your batter aside from sitting there until it's time to use it. It requires an acidic component (buttermilk, yogurt, brown sugar, or vinegar) to react and bubble up with carbon dioxide, the gas that does the rising.

On the other hand, baking powder is baking soda that is already mixed with a dry acid (usually cream of tartar) and a starch buffer to prevent the acid and baking soda from reacting within the package. Because that acid is already built in, baking powder doesn't need you to add a separate acidic ingredient the way plain baking soda does, but it still needs liquid to kick off the reaction, exactly like baking soda does. Neither one reacts without moisture; the difference is simply that baking powder is already carrying its own acid, pre-mixed and ready to go, while baking soda is still waiting for you to supply one. According to a 2026-updated Healthline report, this is also one of the reasons why the two are not a 1:1 substitution in a recipe, despite their identical appearance when placed side by side on a shelf.

The fix: rebuilding what baking powder already does for you

The vinegar-milk trick is based on the principle of creating baking powder from the ingredients you already have in your refrigerator, instead of using a cream-of-tartar sachet. The vinegar or lemon juice substitutes for the missing acid, the baking soda for the base, and the milk serves as the catalyst or the "liquid" to start the release of carbon dioxide.

Mix it right before adding it to the batter; the reaction begins when the acid comes in contact with the soda, not when it's put in the pan and placed in the oven. This isn't a trendytrendy life hack that came out this past week either. A similar principle, cream of tartar and baking soda in place of baking powder, is listed as a standard, tested option in place of baking powder in a 2025 Randolph County Center article.

Looks like a lot of confident home bakers do this: eyeballing it. Chemistry depends on the right ingredients in the right proportions. If you don't use enough baking soda, your cake will be grumpy and flat; too much and you'll have an aftertaste of bitterness and faint soapiness. The measurements above are for approximately one teaspoon of commercial baking powder; if a recipe calls for more, scale the baking soda, acid, and milk proportionally rather than just adding "a bit more" soda on its own, and remember to cut the recipe's other liquid by whatever amount of milk you use in the substitute, so you don't end up over-hydrating the batter.

The part no one talks about

This replacement is very useful, but it's not a complete copy of the original. The additional liquid and mild acidic tang that a neutral cake batter wasn't designed to handle is best suited to recipes where some indulgence is acceptable, such as pancakes, quick breads, biscuits and muffins, but not delicate and pale sponge cake where flavor and crumb are paramount. Once the acid hits the soda, the reaction starts immediately, so don't let the batter sit around, get it into the oven while it's still actively bubbling.

When baking powder goes missing, it's not as big a deal at 9 pm as it looks. It is the same chemistry that does what chemistry does: a base seeking an acid to react with, and it's likely that you already have both in your fridge. Stay within the proportions, use it quickly, and reserve this for those recipes that will accept a little bit of imperfection. Either way, your Sunday bake may still turn out well.