A married person has a 1 in 365.25 chance (including leap years) of sharing their birthday with their partner. With approximately 11.6 million married couples in the UK, around 31,750 married couples in the UK share a birthday.
The commonest age gap between British spouses is one year. Two years is the average (mean), but nearly 1 in 10 UK marriages are between people born in the same year. So 3,000 or so UK married couples can share one birthday cake, with the same number of candles.
Birthdays aren't evenly spread throughout the year. A recent Harvard study shows 21 of the 30 commonest birthdays are in September (in the USA). So being born in September gives you a bigger pool of potential joint-birthday partners. But things were different for the Huntrodds. September wasn't necessarily the most popular birth month in 17th century England.
So if your birthday is also September 19th, your odds of marrying somebody with the same birthday are probably higher today than they were for Frances and Mary Huntrodds.