What if you'd held PRTA?
A $1,000 investment in Prothena Corporation plc (PRTA) at the month-end close of 2012-12 would be worth $1,267 at the close of 2026-08 — +26.7% total return, dividends reinvested. The same $1,000 in the S&P 500 would be worth $5,405.
Your scenario
Result
If you'd bought $1,000 at the start of each year
Value of $1,000 invested on January 1 of each year, held to 2026-08, dividends included.
Every year, $1,000 from 2012
| Year | Value of $1,000 | Year return |
|---|---|---|
| 2012 | $1,000 | — |
| 2013 | $3,618 | +261.8% |
| 2014 | $2,832 | -21.7% |
| 2015 | $9,292 | +228.1% |
| 2016 | $6,711 | -27.8% |
| 2017 | $5,115 | -23.8% |
| 2018 | $1,405 | -72.5% |
| 2019 | $2,160 | +53.7% |
| 2020 | $1,638 | -24.1% |
| 2021 | $6,739 | +311.3% |
| 2022 | $8,220 | +22.0% |
| 2023 | $4,958 | -39.7% |
| 2024 | $1,889 | -61.9% |
| 2025 | $1,303 | -31.0% |
| 2026 | $1,267 | -2.7% |
Best and worst month-end to buy
The best single month-end close to have bought PRTA was 2025-05 ($4.59): $1,000 then is $2,024 today. The worst was 2021-09 ($71.23): $1,000 then is $130.
FAQ
What would $1,000 in PRTA be worth today?
A $1,000 investment in Prothena Corporation plc (PRTA) at the start of 2012 would be worth about $1,267 today, a total return of +26.7%. Dividends are reinvested in these figures.
What were the best and worst years for PRTA?
Prothena Corporation plc (PRTA)'s strongest calendar year since 2012 was 2021, a +311.3% return — $1,000 held through that year became about $4,113 by year-end. Its weakest year was 2018, at -72.5%.
Does the calculator include dividends and splits?
Yes where available. Prices are adjusted for both stock splits and reinvested dividends (total return), the same measure brokerages use.
How much would $100 per month in PRTA have grown?
Investing $100 at the end of every month since 2012-12 would have grown to about $8,564 on $16,500 invested.
Did PRTA beat the S&P 500?
Over the same period, $1,000 in the S&P 500 index would be worth $5,405. PRTA trailed the S&P 500 by +76.5% in total return.
Is this investment advice?
No. Wall Street Regrets is an entertainment and education tool. Every number is a historical calculation, not a prediction, and past performance never guarantees future results.
Methodology
Prothena Corporation plc (PRTA) historical total-return data from 2012-12 to 2026-08, reduced to month-end closes for the tables above.
Returns use adjusted close prices from Yahoo Finance historical data — adjusted for stock splits and reinvested dividends — the same convention used by major brokerages. A "year" scenario invests $1,000 at the prior December's month-end close and values it at the latest available month-end close. Non-USD amounts are converted at historical month-end exchange rates (Yahoo Finance): to USD on the buy date and back to your currency at the latest rate, so the return reflects the currency move as well as the asset.
Month-end resolution means intra-month extremes are not captured in tables; the calculator uses exact trading-day closes where daily data is available. Figures ignore taxes, fees, and the currency effects of non-USD listings. History is not a forecast. Wall Street Regrets is entertainment, not investment advice.
What if you'd held…
Data: adjusted close prices via Yahoo Finance. As of 2026-08. Not financial advice.