To determine a birthstone, look up the calendar month of a birth date on both the modern list and the traditional list, because the two lists disagree on several months. Birthstones are assigned by month, not by day, so the exact day in a birth date never changes the answer. The modern list descends from one adopted by American jewellers in 1912 and has been revised in documented steps since, favouring transparent faceted gems and adding alexandrite, tourmaline, citrine and zircon in 1952, tanzanite in 2002, and spinel in 2016. Traditional lists reflect older custom and disagree from reference to reference, so an honest answer marks which traditional stones are documented by more than one source rather than picking one house version and presenting it as settled. Six months on the modern list also legitimately carry more than one stone, and collapsing them to a single gem is the single most common error in any birthstone chart you find online.
Why a single-gem answer is usually wrong
Most birthstone charts online are tidier than the data behind them. They print one gem per month and leave it at that, which makes the table look neat and the answer look settled. It is neither. Six months on the current list legitimately carry more than one stone, and the Birthstone Finder keeps all of them visible rather than choosing for you.
- March: aquamarine and bloodstone
- June: pearl, alexandrite and moonstone
- August: peridot, spinel and sardonyx
- October: opal and tourmaline
- November: topaz and citrine
- December: turquoise, tanzanite and zircon
If you were born in any of those months, the chart that prints only one gem has just hidden part of your answer. The current list is published by both the Gemological Institute of America and the American Gem Society, and the two references were compared month by month and agree on all of the multi-stone months. Charts that flatten them to a single entry are simplifying for visual convenience, not for accuracy.
Modern versus traditional birthstones
The single word "birthstone" hides two different things, and confusing them is the second most common error after the single-gem simplification. The modern list is the one most readers are given. It was adopted by the American National Association of Jewelers in 1912 and has been amended in three documented rounds since. Modern charts tend to favour transparent faceted gems and have a relatively small, consistent set of stones that has been refined over more than a century. The traditional list is older and reflects a different historical lineage, with more opaque stones, a stronger religious and calendrical context, and significantly more variation between references.
A consequence that matters when you read any birthstone chart: traditional sources do not agree with each other. Some circulating versions even include stones that could not have been traditional at all. Rather than pick one house version and present it as settled, the Birthstone Finder shows the modern column from GIA and AGS side by side and, on the traditional side, shows only the stones that two independent gemological references both list. Where the two lists disagree, that disagreement is the interesting part. For March, the documented traditional answer is bloodstone rather than the modern aquamarine. For August, it is sardonyx rather than peridot. For December, it is turquoise and lapis lazuli rather than tanzanite and zircon.
Determine your birthstone in three steps
The lookup itself is straightforward. Using the Birthstone Finder, follow these three steps.
- Select a birth month from the list, or use the optional date field and the month will be filled in for you. The date field accepts an ISO-style date, parses it, and rejects impossible entries, including February 29 outside a leap year. It exists purely so you can paste a birthday you already have rather than work out which month to select.
- Read the modern birthstones first, remembering that six months legitimately carry more than one stone. If your month is one of March, June, August, October, November or December, the modern column will list more than one gem, and all of them are your answer, not a tie-breaker the chart has to choose for you.
- Compare against the traditional row, and check the addition note to see which modern stones arrived in 1952, 2002 or 2016. The traditional row shows only stones that two independent references both list, and the addition note records the documented year for each modern stone where one is sourced.
That is the full method. The lookup runs in the browser, so nothing you enter is uploaded, stored, or logged.
When each modern stone was officially added
The modern list is not ancient. It has a history, and the additions have dates. The Birthstone Finder shows the addition year for every modern stone where one is documented; stones with no sourced year carry no date, because inventing a plausible year would be worse than leaving the field blank. The documented additions are listed in the table below.
| Stone | Month added to | Year |
|---|---|---|
| Alexandrite | June | 1952 |
| Tourmaline | October | 1952 |
| Citrine | November | 1952 |
| Zircon | December | 1952 |
| Tanzanite | December | 2002 |
| Spinel | August | 2016 |
Per the National Jeweler history of the birthstone list, the 1912 list was the foundation and these revisions are the documented steps that followed. Stones that have been on the list since 1912, such as garnet for January or amethyst for February, carry no addition year because none was needed. The Birthstone Finder does not invent one.
Where the modern and traditional lists differ
The disagreement between lists is not random. It tends to come down to specific substitutions, and the Birthstone Finder shows those substitutions rather than hiding them. The following table summarises the months where the modern list and the documented traditional list genuinely differ, with both columns drawn directly from the Birthstone Finder's two-row output.
| Month | Modern stones (GIA / AGS) | Traditional stones (intersection) |
|---|---|---|
| March | Aquamarine, bloodstone | Bloodstone |
| August | Peridot, spinel, sardonyx | Sardonyx |
| December | Turquoise, tanzanite, zircon | Turquoise, lapis lazuli |
In March, bloodstone was the older choice and aquamarine is the modern addition. In August, sardonyx was the older choice and peridot was added later, with spinel only joining in 2016. In December, the older choice was turquoise and lapis lazuli, with zircon replacing lapis lazuli in 1952 and tanzanite added in 2002. The Birthstone Finder's modern column reflects the current GIA and AGS charts, which the American Gem Society lists openly for anyone who wants a second reference.
What the date field does and does not change
Birthstones are assigned by calendar month, so the exact day never changes which gem appears. A reader born on June 1 and a reader born on June 30 are both reading the same June row, and the Birthstone Finder will produce identical results for both. The optional date field exists for one reason: to let you paste a birthday you already know, rather than work out which month to select. The page parses an ISO date, validates that the day actually exists in that month, including rejecting February 29 outside a leap year, and then uses only the month portion.
There is no day-level birthstone standard, and the tool does not pretend otherwise. Zodiac-sign birthstone lists are a separate and much less settled tradition, and they are not mixed into the modern or traditional columns here. If you want a zodiac-based list, it is a different question and a different chart.
Limits of this method
A few deliberate limits are worth stating up front. First, the modern list is itself a cultural and commercial convention, not a natural fact, and the Birthstone Finder is offered for cultural interest rather than as a hard rule. For a purchase, confirm the stone and its treatment with a qualified jeweller or a gemological laboratory report. Second, the lookup runs entirely in the browser, so nothing you enter is uploaded, stored, or logged; the answer is yours alone, and you can verify it by reopening the page tomorrow on the same month. Third, the answer for a given month does not change between visits, because the underlying tables are fixed references rather than a daily draw. Birthstones do not rotate. If a chart ever appears to give you a different answer for the same month on a different day, the chart is wrong, not the stones.
Putting those limits together, the working method is simple: take the month from a birth date, read the modern row first with attention to whether it lists more than one stone, then read the traditional row for the documented older choice, and finally check the addition note for any stone that was officially added in 1952, 2002 or 2016. That is how to determine a birthstone without being misled by a chart that flattens the answer.