A friend showed up to my apartment once carrying a five gallon bucket of what looked like grated parmesan. “Laundry detergent,” she said. “Three months’ worth. Cost me four dollars.” She had been making her own for years and swore it cleaned better than the stuff she used to buy.

I was skeptical. Homemade laundry soap sounded like a project for people who also make their own yogurt and knit their own socks. But the math was hard to argue with: about four cents per load versus twenty to thirty cents for store-bought. Over a year of laundry for two people, that’s real money.

The basic recipe

You need three ingredients, all available in the laundry aisle of any grocery store or big box retailer:

One bar of laundry soap (Fels-Naptha, Zote, or Castile) — about $1. Grate it finely with a cheese grater. Dedicate a grater to this; you don’t want soap residue in your mac and cheese.

One cup of washing soda (not baking soda — washing soda is sodium carbonate, stronger and more alkaline). About $4 for a box that’ll last you a year.

One cup of borax. Another $4 box that lasts forever.

How to make it

Mix the grated soap, washing soda, and borax together in a large bowl or bucket. Stir well. Transfer to an airtight container. Use one to two tablespoons per load depending on how dirty the clothes are.

That’s it. No cooking, no boiling, no blending. Five minutes of grating and stirring for months of detergent. It’s a dry powder so it doesn’t spoil.

Does it actually work?

For everyday laundry — t-shirts, jeans, towels, sheets — yes, it works. The soap provides the cleaning action, the washing soda boosts the soap’s effectiveness and softens water, and the borax helps with stains and odor. It doesn’t produce suds the way commercial detergents do, which throws people off at first. Suds are not cleaning. Suds are marketing.

For heavily soiled items — gym clothes, work uniforms, cloth diapers — you might want a booster. Add half a cup of white vinegar to the rinse cycle. It helps remove any soap residue and cuts through lingering odors.

When to skip it

If you have a high-efficiency (HE) washer, check your manual. Some manufacturers say homemade detergents can cause buildup. HE machines use less water, so soap residue has a harder time rinsing out. If your HE washer starts smelling musty after switching, go back to HE-specific detergent.

Also: homemade detergent is soap-based, not detergent-based. In hard water areas, soap can react with minerals to form a residue called soap scum. If you notice whites turning gray or towels feeling stiff, your water is too hard for homemade detergent.