Estimating the total number of stars that have ever existed in the universe is a challenging task and subject to uncertainties. The current scientific understanding suggests that the majority of stars in the universe have not yet formed.
The universe is approximately 13.8 billion years old, and star formation has been occurring since relatively early in its history. However, star formation continues to take place today, and there are vast regions of interstellar gas and dust available for future star formation.
While it is difficult to provide an exact percentage, it is unlikely that 95% of all stars that will ever exist have already formed. There are still numerous galaxies, nebulae, and star-forming regions where new stars continue to emerge. The total number of stars in the universe is expected to increase over time as more star formation occurs.
It's important to note that our understanding of the universe is continually advancing, and new discoveries can refine our estimates. Therefore, the precise percentage of stars that have already formed versus those that will form in the future may be subject to revision based on future scientific research and observations.