diff --git a/conservancy_beancount/books.py b/conservancy_beancount/books.py
new file mode 100644
index 0000000..300bfac
--- /dev/null
+++ b/conservancy_beancount/books.py
@@ -0,0 +1,74 @@
+"""books - Tools for loading the books"""
+# Copyright © 2020  Brett Smith
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import datetime
+
+from typing import (
+    Iterable,
+    NamedTuple,
+    Optional,
+    Union,
+)
+
+class FiscalYear(NamedTuple):
+    month: int = 3
+    day: int = 1
+
+    def for_date(self, date: Optional[datetime.date]=None) -> int:
+        if date is None:
+            date = datetime.date.today()
+        if (date.month, date.day) < self:
+            return date.year - 1
+        else:
+            return date.year
+
+    def range(self,
+              from_fy: Union[int, datetime.date],
+              to_fy: Union[int, datetime.date, None]=None,
+    ) -> Iterable[int]:
+        """Return a range of fiscal years
+
+        Both arguments can be either a year (represented as an integer) or a
+        date. Dates will be converted into a year by calling for_date() on
+        them.
+
+        If the first argument is negative or below 1000, it will be treated as
+        an offset. You'll get a range of fiscal years between the second
+        argument offset by this amount.
+
+        If the second argument is omitted, it defaults to the current fiscal
+        year.
+
+        Note that unlike normal Python ranges, these ranges include the final
+        fiscal year.
+
+        Examples:
+
+          range(2015)  # Iterate all fiscal years from 2015 to today, inclusive
+
+          range(-1)  # Iterate the previous fiscal year and current fiscal year
+        """
+        if not isinstance(from_fy, int):
+            from_fy = self.for_date(from_fy)
+        if to_fy is None:
+            to_fy = self.for_date()
+        elif not isinstance(to_fy, int):
+            to_fy = self.for_date(to_fy - datetime.timedelta(days=1))
+        if from_fy < 1:
+            from_fy += to_fy
+        elif from_fy < 1000:
+            from_fy, to_fy = to_fy, from_fy + to_fy
+        return range(from_fy, to_fy + 1)
diff --git a/tests/test_books_fiscal_year.py b/tests/test_books_fiscal_year.py
new file mode 100644
index 0000000..9327ab0
--- /dev/null
+++ b/tests/test_books_fiscal_year.py
@@ -0,0 +1,136 @@
+"""test_books_fiscal_year - Unit tests for books.FiscalYear"""
+# Copyright © 2020  Brett Smith
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import datetime
+import itertools
+
+import pytest
+
+from conservancy_beancount import books
+
+@pytest.fixture(scope='module')
+def conservancy_fy():
+    return books.FiscalYear(3, 1)
+
+@pytest.fixture(scope='module')
+def cy_fy():
+    return books.FiscalYear(1, 1)
+
+# Not bothering because it's too much trouble to override __new__
+# @pytest.mark.parametrize('month,day', [
+#     (0, 0),
+#     (2, 29),
+#     (4, 31),
+#     (13, 15),
+#     (-1, 1),
+#     (1, -5),
+# ])
+# def test_values_checked(month, day):
+#     with pytest.raises(ValueError):
+#         books.FiscalYear(month, day)
+
+def test_attribute_access():
+    fy = books.FiscalYear(2, 15)
+    assert fy.month == 2
+    assert fy.day == 15
+    with pytest.raises(AttributeError):
+        fy.year
+
+@pytest.mark.parametrize('month,day,expected', [
+    (1, 1, 2019),
+    (2, 15, 2019),
+    (2, 28, 2019),
+    (2, 29, 2019),
+    (3, 1, 2020),
+    (3, 9, 2020),
+    (6, 1, 2020),
+    (12, 31, 2020),
+])
+def test_for_date(conservancy_fy, month, day, expected):
+    date = datetime.date(2020, month, day)
+    assert conservancy_fy.for_date(date) == expected
+
+def test_for_date_default_today(cy_fy):
+    assert cy_fy.for_date() == datetime.date.today().year
+
+@pytest.mark.parametrize('begin_date,end_date,expected', [
+    ((2020, 3, 1), (2021, 2, 28), [2020]),
+    ((2020, 1, 1), (2020, 3, 1), [2019]),
+    ((2020, 1, 1), (2020, 3, 5), [2019, 2020]),
+    ((2019, 2, 1), (2020, 6, 1), [2018, 2019, 2020]),
+])
+def test_range_two_dates(conservancy_fy, begin_date, end_date, expected):
+    actual = list(conservancy_fy.range(datetime.date(*begin_date), datetime.date(*end_date)))
+    assert actual == expected
+
+@pytest.mark.parametrize('year_offset', range(3))
+def test_range_one_date(cy_fy, year_offset):
+    this_year = datetime.date.today().year
+    actual = list(cy_fy.range(datetime.date(this_year - year_offset, 1, 1)))
+    assert actual == list(range(this_year - year_offset, this_year + 1))
+
+@pytest.mark.parametrize('begin_year,end_year', [
+    (2006, 2020),
+    (2019, 2020),
+    (2020, 2020),
+])
+def test_range_two_years(conservancy_fy, begin_year, end_year):
+    actual = list(conservancy_fy.range(begin_year, end_year))
+    assert actual == list(range(begin_year, end_year + 1))
+
+@pytest.mark.parametrize('year_offset', range(3))
+def test_range_one_year(cy_fy, year_offset):
+    this_year = datetime.date.today().year
+    actual = list(cy_fy.range(this_year - year_offset))
+    assert actual == list(range(this_year - year_offset, this_year + 1))
+
+@pytest.mark.parametrize('year_offset,month_offset', itertools.product(
+    range(-3, 3),
+    [-1, 1]
+))
+def test_range_offset_and_date(conservancy_fy, year_offset, month_offset):
+    end_date = datetime.date(2020, conservancy_fy.month + month_offset, 10)
+    base_year = end_date.year
+    if month_offset < 0:
+        base_year -= 1
+    if year_offset < 0:
+        expected = range(base_year + year_offset, base_year + 1)
+    else:
+        expected = range(base_year, base_year + year_offset + 1)
+    actual = list(conservancy_fy.range(year_offset, end_date))
+    assert actual == list(expected)
+
+@pytest.mark.parametrize('year_offset,year', itertools.product(
+    range(-3, 3),
+    [2010, 2015],
+))
+def test_range_offset_and_year(conservancy_fy, year_offset, year):
+    if year_offset < 0:
+        expected = range(year + year_offset, year + 1)
+    else:
+        expected = range(year, year + year_offset + 1)
+    actual = list(conservancy_fy.range(year_offset, year))
+    assert actual == list(expected)
+
+@pytest.mark.parametrize('year_offset', range(-3, 3))
+def test_range_offset_only(cy_fy, year_offset):
+    year = datetime.date.today().year
+    if year_offset < 0:
+        expected = range(year + year_offset, year + 1)
+    else:
+        expected = range(year, year + year_offset + 1)
+    actual = list(cy_fy.range(year_offset))
+    assert actual == list(expected)