The short answer
Around half what the cap suggests, and less again in a soft water area. Excess detergent does not rinse out, and it leaves a residue that holds dirt and smells.
- Start at half the recommended dose and only go up if things are coming out visibly unclean.
- Use less in a soft water area. Dosing instructions assume hard water, where much of the detergent is consumed neutralising minerals rather than cleaning.
- Never fill the drum more than three quarters. Clothes need room to move through the water, and an overfilled drum washes badly at any dose.
- If clothes feel stiff or smell musty, you are using too much, not too little.
What will ruin it
Liquid detergent at low temperatures is a common cause of a smelly machine, because it does not dissolve fully and leaves deposits. Powder is better for maintenance washes.
Why it works
The dosing on a bottle is set for a heavily soiled full load in hard water, which is almost never the load in front of you. The manufacturer has no incentive to err low.
Household chemicals can be dangerous in combination. Never mix them, keep the room ventilated, and test anything on a hidden patch first. Full disclaimer.
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