Leveling System - Carry extra XP over to next Level

I am creating a basic Levelling system however I have hit a bit of a snag, this is more of a Math problem than a Java one. I would like to dynamically carry over any additional XP over to the next level, currently once the Level up requirement has been it, the XP count simply gets set to 0. Please note that I would like this to be able to handle the use case if the Player gets enough XP to go up several levels at once.

My current code is below :

	public void giveXP(String name, int xp) {
		
	int pXP = Main.storedUsers.get(name).getXP();
	
	this.xp = (pXP + xp);
	
	int pLevel = Main.storedUsers.get(name).getLevel();
	double constant = 2;
	double fixed = 450;
	int nextLevelXP = Math.round((pLevel * constant) + fixed);
	int xpNeededToLevelUp = nextLevelXP - pXP;
	
	if (xpNeededToLevelUp > 0) {
		Admin.debugMessage("You gained " + xp + " XP, "+ xpNeededToLevelUp + " needed for next Level.");			
	}
	
	else if (xpNeededToLevelUp <= 0) {
		Admin.debugMessage(name + " leveled up to level " + (pLevel+1));
		UserFetch.setLevel(name, (pLevel+1));
		Main.storedUsers.get(name).setLevel(pLevel+1);
		this.xp = 0;
	}
}

Just to update how I solved the issue I was having while also being able to handle multiple level ups at once, the code is below : (The only issue is the small XP gaps in lower levels but that is a math issue)

	public static int getLevelXPThreshold(int level) {
	int value = (int) (75+(400+(75*(Math.pow(1.10409,level)))));
	return value;
}

		
public static Map<Integer, Integer> getXPThresholds() {
	
	int maxLevel = 90;
	
	Map<Integer, Integer> levelXPThresholds = new HashMap<Integer, Integer>();


	for (int level = 1; level < maxLevel; level++) {
		int levelXP = getLevelXPThreshold(level);
		levelXPThresholds.put(level, levelXP);
	}
	
	return levelXPThresholds;
}

public static int canUserLevelUp(User user) {
	
	int xp = user.getXp();
	
	Map<Integer, Integer> levelXPThresholds = getXPThresholds();

	for (int levels : levelXPThresholds.keySet()) {
		
		if (!(xp >= levelXPThresholds.get(levels))) { 
								
			if (user.getLevel() != levels) {
				
				UserFetch.setLevel(user.getName(), (levels));
				Main.storedUsers.get(user.getName()).setLevel(levels);
			}
			
			int nextLevelXP = getLevelXPThreshold(levels); //<--- this means it will always return the level higher than the current user level based on xp value.
			
			return nextLevelXP -= xp;
			
		}
	}
	
	return 0;
}