diff --git a/src/ballot.rs b/src/ballot.rs
index 1c8b3a9..3001ce5 100644
--- a/src/ballot.rs
+++ b/src/ballot.rs
@@ -57,11 +57,9 @@ impl Ballot {
 	pub fn apply_weight(&mut self, weight: f64) {
 		self.weight *= weight;
 	}
-	pub fn get_primary_index<F>(&self, enabled: F) -> Option<usize>
-		where F: Fn(usize) -> bool
-	{
+	pub fn get_primary_index(&self, enabled: &[bool]) -> Option<usize> {
 		for &id in self.votes.iter() {
-			if enabled(id) {
+			if enabled[id] {
 				return Some(id);
 			}
 		}
diff --git a/src/counter.rs b/src/counter.rs
index 7c55396..7d06779 100644
--- a/src/counter.rs
+++ b/src/counter.rs
@@ -1,4 +1,4 @@
-use std::rc::Rc;
+use std::{sync::{atomic::{AtomicUsize, Ordering}, mpsc, Arc, Mutex}, thread};
 use itertools::Itertools;
 
 use crate::{ballot::Ballot, header::Header, stats::Stats, util::ScoreItem};
@@ -11,7 +11,7 @@ pub enum Event {
 
 #[derive(Debug)]
 pub struct Counter {
-	pub header: Rc<Header>,
+	pub header: Arc<Header>,
 	pub ballots: Vec<Ballot>,
 	pub stats: Stats,
 	winners_left: usize,
@@ -21,7 +21,7 @@ pub struct Counter {
 
 impl Counter {
 	pub fn new<T: std::io::BufRead>(mut csv: quick_csv::Csv<T>, winners: usize) -> Result<Self, Box<dyn std::error::Error>> {
-		let header = Rc::new(Header::parse(csv.next().ok_or("csv header missing")??, winners)?);
+		let header = Arc::new(Header::parse(csv.next().ok_or("csv header missing")??, winners)?);
 		let mut ballots = Vec::new();
 		let mut stats = Stats::new();
 
@@ -47,17 +47,55 @@ impl Counter {
 		})
 	}
 	fn count_primaries(&self) -> Vec<ScoreItem> {
-		let mut scores = vec![0.0; self.enabled.len()];
-		for ballot in self.ballots.iter() {
-			if let Some(index) = ballot.get_primary_index(|id| self.enabled[id]) {
-				scores[index] += ballot.get_weight();
+		let mut scores = Mutex::new(vec![0.0; self.enabled.len()]);
+		let ballot_chunks = Mutex::new(self.ballots.chunks(1024));
+
+		thread::scope(|s| {
+			let threads = std::thread::available_parallelism().unwrap().into();
+			for _ in 0..threads {
+				s.spawn(|| {
+					let mut l_scores = vec![0.0; self.enabled.len()];
+					while let Some(ballots) = { ballot_chunks.lock().unwrap().next() } {
+						for ballot in ballots {
+							if let Some(index) = ballot.get_primary_index(&self.enabled) {
+								l_scores[index] += ballot.get_weight();
+							}
+						}
+					}
+					for (dst, src) in scores.lock().unwrap().iter_mut().zip(l_scores.into_iter()) {
+						*dst += src;
+					}
+				});
 			}
-		}
-		scores.into_iter().enumerate().filter_map(|(index, value)| match self.enabled[index] {
+		});
+
+		scores.get_mut().unwrap().iter().copied().enumerate().filter_map(|(index, value)| match self.enabled[index] {
 			true => Some(ScoreItem::new(index, value)),
 			false => None,
 		}).collect_vec()
 	}
+	fn apply_weights(&mut self, winners: &[ScoreItem]) {
+		let ballot_chunks = Mutex::new(self.ballots.chunks_mut(1024));
+		thread::scope(|s| {
+			let threads = std::thread::available_parallelism().unwrap().into();
+			for _ in 0..threads {
+				s.spawn(|| {
+					while let Some(ballots) = { ballot_chunks.lock().unwrap().next() } {
+						for ballot in ballots {
+							let index = match ballot.get_primary_index(&self.enabled) {
+								Some(v) => v,
+								None => continue,
+							};
+							if let Some(winner) = winners.iter().filter(|&v| v.index == index).next() {
+								let surplus = winner.value - self.quota;
+								ballot.apply_weight(surplus / winner.value);
+							}
+						}
+					}
+				});
+			}
+		});
+	}
 	pub fn get_quota(&self) -> f64 {
 		self.quota
 	}
@@ -89,19 +127,9 @@ impl Iterator for Counter {
 		}
 
 		winners.sort_by(|a,b| b.cmp(a));
-
-		for ballot in self.ballots.iter_mut() {
-			let index = match ballot.get_primary_index(|id| self.enabled[id]) {
-				Some(v) => v,
-				None => continue,
-			};
-			if let Some(winner) = winners.iter().filter(|&v| v.index == index).next() {
-				let surplus = winner.value - self.quota;
-				ballot.apply_weight(surplus / winner.value);
-			}
-		}
-
+		self.apply_weights(&winners);
 		self.winners_left -= winners.len();
+
 		for winner in winners.iter() {
 			self.enabled[winner.index] = false;
 		}