Score is adding a life on first kill. I want it to add only after a certain amount of points.

I’m really new to unity and programming. I finished the Space Shooter tutorial and have began making additions to the script. I’m trying to add a life after every 1000 point the player earns, it’s working good with the exception that it adds a life after the very first kill and then every 1000 points after.
can someone please help me, not just with the code but also explain what I’m doing wrong and you it’s acting the way it is.

here is what I have.

public void AddScore(int newScoreValue)
{
    score += newScoreValue;
    UpdateScore();

    if(score >= plusLives)
    {
        plusLives = plusLives + 1000;// adding 1 on first kill for some reason.
        playerLives++;
        Debug.Log(plusLives);
    }

}

void UpdateScore()
{
    scoreText.text = "Score: " + score;


}

The only thing I can think of, is your plusLives is set to 0 initially.

So, after that first kill,

score >= plusLives would be true, since plusLives is 0.