How to calculate age by input field date on the frontend?

Question

I have a model which has a field called public DateTime birthday {get ; set; } = DateTime.Today; public int age = 0; My Razor file

so what I am trying to do is some front end validation. If the person is less than 50 years old, I want to display a message saying "Sorry you are too young" (or anything).

Rufus L · Accepted Answer

Age should not be stored data - it's a calculated value based on the time of the query; therefore I would recommend making it a read-only property that's calculated on the fly:
public DateTime Birthday { get; set; } = DateTime.Today;

public int Age
{
    get
    {
        var today = DateTime.Today;
        var age = today.Year - Birthday.Year;
        if (Birthday.Date > today.AddYears(-age)) age--;
        return age;
    }
}

Now you have a calculated field that will give the accurate Age (in years), which you can then use to compare against 50.
Note that the age calculation comes from this answer.

How to calculate age by input field date on the frontend?

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