You say it, and the answer is: “Then tell me what to do.” That's where the conversation stalls every time, and there's a reason.
You say you're running on empty. Your partner says: “Then tell me what to do.” He means it, it exhausts you, and neither of you understands why the other reacts so oddly.
That conversation stalls because you're talking about two different things.
The part you carry is made of things that never happen where anyone can see them. Working out that swimming lessons need arranging. Noticing the coat is getting too small. Remembering a present is needed on Saturday and that this child likes dinosaurs.
That work leaves no traces. You can see a clean kitchen; you can't see the decision to do pasta tonight because there was a courgette left and nobody had time. Researchers call this the cognitive part of household labour, and it's by definition invisible to whoever isn't doing it.1
So when he says he doesn't see it, he is probably not lying. He can't see it, because there's nothing to see.
Almost nobody chooses this. The mechanism is that whoever does something once becomes the person who does it from then on.
Answer the school email once and you're the person who reads the school email. Remember one birthday and you remember them all from then on. Every time it makes sense, because you already know.
On top of that, you can do it faster than explain it. Explaining what needs doing, how, when and where things are kept costs more effort than just sorting it. So you sort it, and confirm once again that you're the one who knows.
That offer takes over the doing. That's step five. The steps before it stay exactly where they were: seeing that something will be needed, identifying options, deciding, and monitoring whether it happened.1
In fact the work grows. Now you also have to explain and then check. Whoever asks what to do is asking you to stay the manager. More on that here.
As long as it's your feeling against his, nobody wins. What helps is putting something concrete between you that neither of you can argue with.
Not "I do everything", but: here are the twelve recurring things in our household, and here is who thinks about them. Then it's no longer about who feels more burdened, but about a list you both look at.
That's exactly what the test is for. Twelve questions, two minutes, each of you separately. The two results side by side are the conversation you otherwise never manage to have.
Often that's true. The trap is that doing a lot and carrying the load are two different things.
Someone can cook three evenings a week and carry not an ounce of mental load, as long as somebody else works out what gets cooked, whether the shopping is in, and whether to allow for a child who won't eat onion.
That isn't a reproach and not a scoreboard. It's why "we already split things fairly" and "I'm running on empty" can both be true in the same house.
The first instinct is usually: then I will just be more efficient. A better system, a tighter weekly menu, everything prepared in advance. That works for a few weeks and then snaps back.
The reason is simple. Getting more efficient raises how much you can handle, but doesn't lower what's being asked of you. And as long as you hold the overview, the demand grows to match what you can handle. Every time you prove you can cope, something else gets added.
What genuinely tips the scales is carrying less, not carrying better. That's an uncomfortable answer, because carrying less means genuinely handing something over, and that feels at first like letting go of control.
Ask why somebody doesn't hand things over and you often get: "then it won't happen, or not properly". That's a real fear and usually a well-founded one, because at first things do go wrong.
But there's a difference between going wrong once and not working. A forgotten PE kit is annoying and it isn't proof that the handover failed. It's proof that the other person is still learning what you've known for three years.
So the question isn't whether it goes perfectly, but whether you can sit out those first mistakes without taking it back. That's the real work, and it's harder than the PE kit.
That last point is where it usually breaks. One missed appointment and the urge is to take it back. That's exactly where the load gets redistributed, and usually not in your favour.
Why does my partner not see how much I do?
Because most of it's invisible, including to somebody who means well. If you've never worked out that swimming lessons needed arranging, you can't sense how much headspace that took up. It isn't unwillingness but a blind spot that comes with the division itself.
How do I explain mental load to my partner?
Not with "I do everything", because that's one feeling against another. Use something concrete you can both see: a list of twelve recurring things with who thinks about them. Then the conversation is about the list, not about who feels more burdened.
Why does "just tell me what to do" not work?
Because that question makes you the manager. The asker takes over the doing, but the thinking, planning and monitoring stay with you. In practice the work grows: now you also have to explain and check.
Is this a relationship problem?
Usually not in the sense of unwillingness. It's a division that arose without anyone choosing it, and that keeps itself in place. It does make it something to solve together, because working harder on your own doesn't fix it.
Take the test: who keeps track of everything?