diff --git a/README.md b/README.md
index 44707e2..72e47a3 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@ standard output.
 * A small, unix-like utility, designed for use in build scripts.
 * Agnostic to the number of segments.
 * Agnostic to version prefixes, like "v".
+* Compatible with semantic versioning, but does not require it.
 
 ## Installation
 
@@ -30,26 +31,47 @@ Usage of bump:
 
 ```sh
 # default
-echo "1.0.0" | bump  # => 1.0.1
-echo "v1.2" | bump  # => v1.3
-echo "version 42" | bump  # => version 43
+echo "1.0.0" | bump      # => 1.0.1
+echo "v1.2" | bump       # => v1.3
+echo "version 42" | bump # => version 43
 
 # by index
-echo "1.2.3" | bump -s 0  # => 2.0.0
-echo "1.2.3" | bump -s 1  # => 1.3.0
-echo "1.2.3" | bump -s 2  # => 1.2.4, same as default
+echo "1.2.3" | bump -s 0 # => 2.0.0
+echo "1.2.3" | bump -s 1 # => 1.3.0
+echo "1.2.3" | bump -s 2 # => 1.2.4, same as default
+echo "1.2.3" | bump -s 3 # => 1.2.4-rc.1
 
 # semver aliases
-echo "1.2.3" | bump -s major  # => 2.0.0
-echo "1.2.3" | bump -s minor  # => 1.3.0
-echo "1.2.3" | bump -s patch  # => 1.2.4, same as default
+echo "1.2.3" | bump -s major # => 2.0.0
+echo "1.2.3" | bump -s minor # => 1.3.0
+echo "1.2.3" | bump -s patch # => 1.2.4, same as default
+echo "1.2.3" | bump -s pre   # => 1.2.4-rc.1
 ```
 
 ## Cookbook
 
+### Change default segment to bump
+
+By default, `bump` will bump the rightmost segment. The idiomatic way to
+override this behavior is with an alias.
+
+```sh
+alias bump='bump -s 1' # bump the minor segment by default
+```
+
 ### Bump git tag
 
 ```sh
 git tag "$(git describe --abbrev=0 --tags | bump)"
 git push origin --tags
 ```
+
+### Bump tag based on latest commit keyword
+
+If `+major`, `+minor`, `+patch`, or `+pre` are in the most recent commit, bump
+the version according to the keyword, otherwise bump the patch segment.
+
+```sh
+SEGMENT=$(git show -s --format=%s | awk -F'+' 'BEGIN{RS=" "} /\+/ {print $2}')
+bump -s "${SEGMENT:-patch}"
+```
diff --git a/bump.go b/bump.go
index a6bdaf3..d6528b8 100644
--- a/bump.go
+++ b/bump.go
@@ -12,8 +12,10 @@ import (
 )
 
 type version struct {
-	prefix   string
-	segments []int
+	prefix     string
+	segments   []int
+	prerelease string
+	tag        string
 }
 
 type versionParser func(*version, *bufio.Reader) (versionParser, error)
@@ -63,6 +65,8 @@ func parseSegment(s string) (int, error) {
 			return 1, nil
 		case "patch":
 			return 2, nil
+		case "pre":
+			return 3, nil
 		default:
 			return 0, fmt.Errorf("unrecognized segment: '%s'", s)
 		}
@@ -80,56 +84,80 @@ func readInput(reader io.Reader) (string, error) {
 	return strings.TrimSpace(input), nil
 }
 
-func bumpVersion(old string, index int) (string, error) {
-	v, err := parseVersion(old)
+func bumpVersion(s string, index int) (string, error) {
+	v, err := newVersion(s)
 	if err != nil {
 		return "", err
 	}
 
 	if len(v.segments) == 0 {
-		return "", fmt.Errorf("no version segments found in '%s'", old)
-	} else if index >= len(v.segments) {
+		return "", fmt.Errorf("no version segments found in '%s'", s)
+	} else if index > len(v.segments) {
 		return "", fmt.Errorf("segment index out of range: %d", index)
 	} else if index < 0 {
 		index = len(v.segments) - 1
 	}
 
-	v.segments[index]++
-	for index++; index < len(v.segments); index++ {
-		v.segments[index] = 0
-	}
-
-	ret := strings.Builder{}
-	ret.WriteString(v.prefix)
-	for i, seg := range v.segments {
-		ret.WriteString(strconv.Itoa(seg))
-		if i < len(v.segments)-1 {
-			ret.WriteRune('.')
+	if index == len(v.segments) {
+		if v.prerelease == "" {
+			v.segments[len(v.segments)-1]++
+			v.prerelease = "rc.1"
+		} else {
+			var ok bool
+			v.prerelease, ok = bumpLastDigitRun(v.prerelease)
+			if !ok {
+				v.prerelease += ".1"
+			}
+		}
+	} else if index == len(v.segments)-1 && v.prerelease != "" {
+		v.prerelease = ""
+	} else {
+		v.segments[index]++
+		for index++; index < len(v.segments); index++ {
+			v.segments[index] = 0
 		}
+		v.prerelease = ""
 	}
 
-	return ret.String(), nil
+	return v.String(), nil
 }
 
-func parseVersion(s string) (*version, error) {
+func newVersion(s string) (*version, error) {
 	v := &version{}
 	r := bufio.NewReader(strings.NewReader(s))
 	parseState := parseVersionPrefix
 
-	for {
+	for parseState != nil {
 		var err error
 		parseState, err = parseState(v, r)
 		if err != nil {
 			return nil, err
 		}
-		if parseState == nil {
-			break
-		}
 	}
 
 	return v, nil
 }
 
+func (v *version) String() string {
+	var b strings.Builder
+	b.WriteString(v.prefix)
+	for i, seg := range v.segments {
+		b.WriteString(strconv.Itoa(seg))
+		if i < len(v.segments)-1 {
+			b.WriteRune('.')
+		}
+	}
+	if v.prerelease != "" {
+		b.WriteRune('-')
+		b.WriteString(v.prerelease)
+	}
+	if v.tag != "" {
+		b.WriteRune('+')
+		b.WriteString(v.tag)
+	}
+	return b.String()
+}
+
 func parseVersionPrefix(v *version, reader *bufio.Reader) (versionParser, error) {
 	var prefix []rune
 	defer func() { v.prefix = string(prefix) }()
@@ -149,38 +177,105 @@ func parseVersionPrefix(v *version, reader *bufio.Reader) (versionParser, error)
 
 func parseVersionSegments(v *version, reader *bufio.Reader) (versionParser, error) {
 	var segment []rune
+
+	storeSegment := func() {
+		if len(segment) == 0 {
+			return
+		}
+		int, err := strconv.Atoi(string(segment))
+		if err != nil {
+			return
+		}
+		v.segments = append(v.segments, int)
+		segment = []rune{}
+	}
+	defer storeSegment()
+
 	for {
 		r, _, err := reader.ReadRune()
 		if err == io.EOF {
 			return nil, nil
 		}
 
-		if unicode.IsNumber(r) {
-			segment = append(segment, r)
-			if !bufend(reader) {
-				continue
+		switch r {
+		case '.':
+			if len(segment) == 0 {
+				return nil, fmt.Errorf("parse failed: unexpected '.'")
 			}
+			storeSegment()
+			continue
+		case '-':
+			return parseVersionPrerelease, nil
+		case '+':
+			return parseVersionTag, nil
 		}
 
-		if r == '.' && len(segment) == 0 {
-			return nil, fmt.Errorf("parse failed: unexpected '.'")
-		} else if !unicode.IsNumber(r) && r != '.' {
+		if unicode.IsNumber(r) {
+			segment = append(segment, r)
+		} else {
 			return nil, fmt.Errorf("version parse failed: unexpected character: %s",
 				strconv.QuoteRune(r))
 		}
+	}
+}
 
-		int, err := strconv.Atoi(string(segment))
-		if err != nil {
-			return nil, fmt.Errorf("parse failed: %w", err)
+func parseVersionPrerelease(v *version, reader *bufio.Reader) (versionParser, error) {
+	var prerelease []rune
+	defer func() { v.prerelease = string(prerelease) }()
+
+	for {
+		r, _, err := reader.ReadRune()
+		if err == io.EOF {
+			return nil, nil
 		}
+		if r == '+' {
+			_ = reader.UnreadRune()
+			return parseVersionSegments, nil
+		}
+		prerelease = append(prerelease, r)
+	}
+}
 
-		v.segments = append(v.segments, int)
-		segment = []rune{}
+func parseVersionTag(v *version, reader *bufio.Reader) (versionParser, error) {
+	var tag []rune
+	defer func() { v.tag = string(tag) }()
+
+	for {
+		r, _, err := reader.ReadRune()
+		if err == io.EOF {
+			return nil, nil
+		}
+		tag = append(tag, r)
 	}
 }
 
-func bufend(reader *bufio.Reader) bool {
-	_, _, nextErr := reader.ReadRune()
-	_ = reader.UnreadRune()
-	return (nextErr == io.EOF)
+func bumpLastDigitRun(s string) (string, bool) {
+	var digits []rune
+	pos := -1
+	for i, r := range s {
+		if unicode.IsDigit(r) {
+			if i-len(digits) != pos {
+				digits = []rune{}
+				pos = i
+			}
+			digits = append(digits, r)
+		}
+	}
+	if pos < 0 {
+		return s, false
+	}
+
+	int, err := strconv.Atoi(string(digits))
+	if err != nil {
+		// Only digits are added to the run, so this should never happen.
+		panic(fmt.Sprintf("failed to parse digit run: %s", err))
+	}
+	int++
+
+	var b strings.Builder
+	b.WriteString(string([]rune(s)[:pos]))
+	b.WriteString(fmt.Sprintf("%0"+fmt.Sprint(len(digits))+"d", int))
+	b.WriteString(string([]rune(s)[pos+len(digits):]))
+
+	return b.String(), true
 }
diff --git a/bump_test.go b/bump_test.go
index 2238bba..a6ba19a 100644
--- a/bump_test.go
+++ b/bump_test.go
@@ -35,6 +35,10 @@ func TestParseSegment(t *testing.T) {
 		in:  "patch",
 		seg: 2,
 		err: false,
+	}, {
+		in:  "pre",
+		seg: 3,
+		err: false,
 	}}
 
 	for _, tc := range testCases {
@@ -107,6 +111,54 @@ func TestBumpVersion(t *testing.T) {
 		in:  "1.2.3",
 		seg: -1,
 		out: "1.2.4",
+	}, {
+		in:  "1.2.3",
+		seg: 3,
+		out: "1.2.4-rc.1",
+	}, {
+		in:  "1.2.4-rc.1",
+		seg: 3,
+		out: "1.2.4-rc.2",
+	}, {
+		in:  "1.2.4-rc",
+		seg: 3,
+		out: "1.2.4-rc.1",
+	}, {
+		in:  "1.2.4-rc1",
+		seg: 3,
+		out: "1.2.4-rc2",
+	}, {
+		in:  "1.2.4-rc.42",
+		seg: 2,
+		out: "1.2.4",
+	}, {
+		in:  "1.2.3+sometag",
+		seg: 2,
+		out: "1.2.4+sometag",
+	}, {
+		in:  "1.2.3-rc.4",
+		seg: 1,
+		out: "1.3.0",
+	}, {
+		in:  "1.2.3-alpha.6",
+		seg: 0,
+		out: "2.0.0",
+	}, {
+		in:  "version 100.200.300-release-candidate---42+long.tag.with+symbols",
+		seg: 0,
+		out: "version 101.0.0+long.tag.with+symbols",
+	}, {
+		in:  "v1.2.3-rc.1.2.3",
+		seg: 3,
+		out: "v1.2.3-rc.1.2.4",
+	}, {
+		in:  "1.2-rc.002",
+		seg: 2,
+		out: "1.2-rc.003",
+	}, {
+		in:  "version 1---rc.042.1",
+		seg: 1,
+		out: "version 1---rc.042.2",
 	}}
 
 	for _, tc := range testCases {
@@ -124,11 +176,11 @@ func TestBumpVersion(t *testing.T) {
 }
 
 func TestBumpVersionOutOfRange(t *testing.T) {
-	_, err := bumpVersion("1.2.3", 3)
+	_, err := bumpVersion("1.2.3", 4)
 	if err == nil {
 		t.Fatalf("expected error")
 	}
-	want := "segment index out of range: 3"
+	want := "segment index out of range: 4"
 	if err.Error() != want {
 		t.Errorf("want '%s', got '%s'", want, err.Error())
 	}