There are no rules for how much décolletage is appropriate to reveal in a low neckline. Cleavage exposure is a personal choice. Expose what you are comfortable and confident exposing, and get on with your day.
My friends and clients have very different preferences in this regard. Some are comfortable showcasing a lot of cleavage, while others are not. For some, even a hint of cleavage, in any setting, is too much. Some cover cleavage at work, but showcase cleavage on date night, at the beach, or in formal wear. Some are comfortable showcasing a bit of cleavage in professional settings. Others are comfortable showcasing a bit or a lot of cleavage in non-work settings only. Some base their decision on how confident they’re feeling about their bodies, and who their audience is on the day. If they feel self-conscious in any way, or their audience is conservative – they’ll cover up.
Personally, I think some degree of exposed cleavage in the workplace is inevitable if you’re wearing anything but a very high neckline. This despite the addition of a camisole if you have larger bust and are wearing a V-neck or scoop neckline. But high necklines aren’t as flattering on larger busts, fuller figures, and/or shorter necks, which is why the V or scoop neck was worn in the first place. I don’t think women with a curvy figure or larger bust should be penalized, so I think it’s just fine to show a bit of cleavage at work, especially when you went to the effort of adding a camisole to minimize the effect. Camisoles with front lace detailing and adjustable straps do quite a good job of covering cleavage because the lace detailing can be positioned higher on the décolletage.
In non-professional settings, and especially when you’re on holiday, at the beach, by the pool, at home, for date night, or at a dressy event, I think it’s perfectly acceptable to show some or a lot of cleavage. My tip: do the sit-down test in front of the mirror before you head out because necklines tend to fall open when seated.
I have a regular size bust and a very long neck, which means I wear cleavage covering high necklines 90% of the time because the effect is visually more flattering to my eye. I want to shorten the length of my neck, and high necklines do just that. I do wear collared blouses and shirts leaving some top buttons open, in which case I layer a lacy camisole underneath. I wear the cami not because I want to cover cleavage but because I’m a sucker for a bit of pretty lace peeking through from under the neckline of my top. If I preferred lower necklines on my body type, I’d be fine with showing cleavage in non-professional settings. In professional settings I’d probably conceal as much as I could with a camisole, but not worry too much about it beyond that.
Over to you. How much cleavage are you comfortable exposing, and does the setting make a difference?