diff --git a/calculate_coverages.py b/calculate_coverages.py
index 4c9b869..44a0c6d 100644
--- a/calculate_coverages.py
+++ b/calculate_coverages.py
@@ -5,6 +5,7 @@
 from os import path
 import click
 from glob import glob
+from cover import SortedRangeList
 
 @click.command()
 @click.option('-i',"--input", required=True, help="Input: Directory of sam files (files must end in .sam).")
@@ -15,7 +16,7 @@ def calculate_coverages(input, output, database):
     ###################################
     #Calculate coverage of each contig#
     ###################################
-    gotu_dict = defaultdict(set)
+    gotu_dict = defaultdict(SortedRangeList)
     file_list = glob(input + "/*.sam")
     for samfile in file_list:
         with open(samfile.strip(), 'r') as open_sam_file:
@@ -28,8 +29,7 @@ def calculate_coverages(input, output, database):
                 length_string = linesplit[5]
                 length = sum([int(x) for x in re.split("[a-zA-Z]",length_string) if x])
                 #Add range to contig_dict
-                for i in range(location,location+length):
-                    gotu_dict[gotu].add(i)
+                gotu_dict[gotu].add_range(location, location + length - 1)
 
 
     ###################################
@@ -43,8 +43,12 @@ def calculate_coverages(input, output, database):
     #Calculate coverages#
     #####################
     #Make dataframe from dicitonary of coverages of each contig
-    cov = pd.DataFrame({"gotu":list(gotu_dict.keys()),
-                        "covered_length" : [len(x) for x in gotu_dict.values()] } )
+    cov = pd.DataFrame(
+        {
+            "gotu": list(gotu_dict.keys()),
+            "covered_length": [x.compute_length() for x in gotu_dict.values()]
+        }
+    )
     cov= cov.set_index("gotu")
     cov = cov.sort_values("covered_length", ascending=False)
     #Add genome metadata
diff --git a/cover.py b/cover.py
new file mode 100644
index 0000000..71f328e
--- /dev/null
+++ b/cover.py
@@ -0,0 +1,57 @@
+class SortedRangeList:
+    def __init__(self, autocompress=100000):
+        self.ranges = []
+        self.autocompress = autocompress
+        self.since_compressed = 0
+
+    def add_range(self, start, end):
+        self.ranges.append((start, end))
+        self.since_compressed += 1
+        if self.autocompress is not None and \
+                self.since_compressed > self.autocompress:
+            self.compress()
+
+    def compress(self):
+        if self.since_compressed == 0:
+            return
+        # Sort ranges by start index
+        self.ranges.sort(key=lambda r: r[0])
+
+        new_ranges = []
+        start_val = None
+        end_val = None
+
+        for r in self.ranges:
+            if end_val is None:
+                # case 1: no active range, start active range.
+                start_val = r[0]
+                end_val = r[1]
+            elif end_val >= r[0] - 1:
+                # case 2: active range continues through this range
+                # extend active range
+                end_val = max(end_val, r[1])
+            else:  # if end_val < r[0] - 1:
+                # case 3: active range ends before this range begins
+                # write new range out, then start new active range
+                new_range = (start_val, end_val)
+                new_ranges.append(new_range)
+                start_val = r[0]
+                end_val = r[1]
+
+        if end_val is not None:
+            new_range = (start_val, end_val)
+            new_ranges.append(new_range)
+
+        self.ranges = new_ranges
+        self.since_compressed = 0
+
+    def compute_length(self):
+        if self.since_compressed > 0:
+            self.compress()
+        total = 0
+        for r in self.ranges:
+            total += r[1] - r[0] + 1
+        return total
+
+    def __str__(self):
+        return str(self.ranges)
diff --git a/cover_test.py b/cover_test.py
new file mode 100644
index 0000000..8de0678
--- /dev/null
+++ b/cover_test.py
@@ -0,0 +1,68 @@
+from cover import SortedRangeList
+import random
+from time import perf_counter
+
+
+def simple_test():
+    srl = SortedRangeList(autocompress=None)
+    for i in range(9, 0, -2):
+        srl.add_range(i, i)
+    srl.add_range(4, 4)
+    srl.compress()
+    assert(str(srl) == "[(1, 1), (3, 5), (7, 7), (9, 9)]")
+
+
+def stress_test(seed, num_reads):
+    intset = set()
+    srl = SortedRangeList(autocompress=None)
+
+    start_set = perf_counter()
+    random.seed(seed)
+    for i in range(num_reads):
+        read_start = random.randint(0, 10000000)
+        read_len = random.randint(85, 150)
+        for j in range(read_start, read_start + read_len):
+            intset.add(j)
+    print("SET_ADD: ", perf_counter() - start_set)
+
+    start_srl = perf_counter()
+    random.seed(seed)
+    for i in range(num_reads):
+        read_start = random.randint(0, 10000000)
+        read_len = random.randint(85, 150)
+        srl.add_range(read_start, read_start+read_len-1)
+    print("SRL_ADD: ", perf_counter() - start_srl)
+    srl.compress()
+    print("SRL_ADD AND COMPRESS: ", perf_counter() - start_srl)
+    srl_len = srl.compute_length()
+    print("SRL_ADD COMPRESS AND LENGTH: ", perf_counter() - start_srl)
+
+    print(srl_len)
+    print(len(intset))
+    assert(len(intset) == srl_len)
+    print(len(srl.ranges))
+
+
+def multi_compress_test(seed, num_reads):
+    srl = SortedRangeList(autocompress=None)
+
+    for compress_count in [1000, 10000, 100000]:
+        start_srl = perf_counter()
+        random.seed(seed)
+        for i in range(num_reads):
+            read_start = random.randint(0, 10000000)
+            read_len = random.randint(85, 150)
+            srl.add_range(read_start, read_start+read_len-1)
+            if i % compress_count == 0:
+                srl.compress()
+        print(srl.compute_length())
+        print("Compress Counter: ", compress_count,
+              " Performance: ", perf_counter() - start_srl)
+
+
+simple_test()
+seed = 127
+for reads in [1, 10, 100, 1000, 10000, 100000, 1000000]:
+    multi_compress_test(seed, reads)
+for reads in [1, 10, 100, 1000, 10000, 100000, 1000000]:
+    stress_test(seed, reads)