You watched your mother reach for a name that used to come to her instantly, standing on her own porch, in front of two neighbors who have known her for thirty years. She covered for herself the way she always has, with a joke, and the neighbors laughed and let it go. You didn't. You spent the rest of the visit rehearsing sentences you never said.
That's usually how this question actually shows up. Not as a calm decision at a kitchen table, but as the half-second after a small slip in public, when you realize you've been managing what other people see for weeks without ever deciding to.
I Don't Know Who to Tell covers what to actually say and when it's worth getting outside help. Come back here afterward for the wider view.
What's actually happening
The hesitation almost never comes down to logistics. It comes down to control, specifically control over how people will see her from here on. Once you tell someone, you don't get to edit the impression they form. Sometimes it's kind. Sometimes it's pity dressed up as concern. Either way, it's theirs now, not yours.
But there's a decision hiding underneath that one, and it's easy to skip straight past it: does she get a say in this? If she still has the capacity to weigh in, and in early stage she very often does, this isn't only your call. Some people want their closest friends told right away, because pretending costs them more than the diagnosis does. Others want as few people as possible to know for as long as possible, because losing privacy feels like its own loss on top of everything else. Neither instinct is wrong. Finding out which one is hers, if you can still ask her, changes everything that comes after.
Two ways this goes wrong, and the order that avoids both
Wait too long, and behavior that would read as understandable starts reading as rude or distant to people who don't have the context. A missed birthday, a repeated question at dinner, a friend who used to call every week and doesn't anymore. People fill silence with worse explanations than the truth, and you end up managing two problems instead of one: the dementia, and the version of your family other people are quietly constructing without you.
Tell too soon, before you've found your own footing, and other people's fear and advice can crowd out the small bit of clarity you've built. You don't owe anyone the full picture the moment you have it.
None of this assumes agreement in the house. If your mother, or your spouse, wants this kept quiet out of shame or a real fear of how it'll be seen, that resistance deserves weight even when it's inconvenient for you. Pushing past it turns disclosure into a second fight on top of the first one.
A few things worth knowing
You don't owe anyone the whole file. You can tell someone the shape of it, "it's early, and we're still learning what that means," without handing over every symptom you've noticed.
A workplace is its own calculation. What's safe to say to an employer depends on protections that vary by where you live and what she does for work. That one is worth a real conversation with an employment attorney or her HR office before you decide, not a guess.
The telling is often already happening. By the time you're weighing this, people nearby have usually noticed something and built their own explanation for it. The real choice in front of you is rarely secrecy versus disclosure. It's whether you're the one who gets to say, "I wanted you to hear it from me before you noticed it yourself," or whether they get there on their own.
This lives in two places in the Steadier Ground Method. Reach, because deciding who to let in is its own kind of connection, not a technique to perform. And Steady, because the real question underneath the timing isn't logistics, it's how much you can carry alone before you need other hands under you.