This is the question behind almost every consultation about relationships, and it deserves a straight answer: a birth chart cannot tell you whether someone is the one.
Not because the reading would be difficult, but because the question is not astrological. It assumes a single correct person exists and that the chart holds their identity. Neither is something Jyotisha claims. Any astrologer who answers it directly is telling you what you came to hear.
What a chart can do is considerably more useful than that, provided the question is replaced with better ones.
What two charts can actually be compared on
Given accurate birth details for both people — date, exact time, and place — a comparison produces real information across several dimensions.
The condition of each person's 7th house individually, which describes their capacity for partnership independent of who they are with. Moon compatibility, which governs emotional temperament and daily harmony. Mars placement across both charts, which describes how conflict will behave. Venus and Jupiter, which describe affection and shared values. And the dasha sequences of both people, which describe whether the next decade pulls the two of you in the same direction or opposite ones.
That last one is the most neglected and frequently the most decisive.
Better questions than "is this the one"
Each of these is answerable, and each is more useful than the original.
What will this relationship be like under pressure? Mars and Saturn across the two charts answer this fairly precisely.
What will we actually fight about, and will it resolve? The friction profile is readable, and knowing it in advance is worth more than knowing a compatibility score.
Do our timelines align? Two people entering very different life periods experience the same marriage differently, and this is where a great many otherwise well-matched pairs run into trouble.
Is this person capable of sustained partnership at all? An individual reading of their 7th house answers this, and it is a different question from whether the two of you are compatible.
The limit worth respecting
A chart describes tendency, structure and timing. It does not describe choice, effort, or what two people decide to do with what they have been given — and those account for a great deal of how a marriage actually goes.
There are well-matched charts that fail through neglect and difficult ones that work because both people were committed to making them work. Compatibility analysis tells you what the terrain looks like. It does not walk it for you.
What to do with this
If you are asking whether someone is the one, you are usually asking something more specific underneath it — whether you are being naive, whether the difficulty you are seeing is temporary, whether you will regret this. Those are readable.
Bring both charts, ask the narrower question, and accept an answer that comes as a description rather than a yes. It is less dramatic than a verdict and considerably more likely to be true.