diff --git a/datetime/period.go b/datetime/period.go
new file mode 100644
index 0000000..03e3a5c
--- /dev/null
+++ b/datetime/period.go
@@ -0,0 +1,41 @@
+package datetime
+
+import "time"
+
+type Period struct {
+	Begin time.Time `json:"start" yaml:"start"`
+	End   time.Time `json:"end" yaml:"end"`
+}
+
+const maxNsec = 999999999
+
+func NewPeriod(a, b time.Time) Period {
+	return Period{Begin: StartOfDay(a), End: EndOfDay(b)}
+}
+
+func StartOfDay(t time.Time) time.Time {
+	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, time.UTC)
+}
+
+func EndOfDay(t time.Time) time.Time {
+	return time.Date(t.Year(), t.Month(), t.Day(), 23, 59, 59, maxNsec, time.UTC)
+}
+
+func MonthOf(t time.Time) Period {
+	var (
+		begin    = time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, time.UTC)
+		finalDay = time.Date(t.Year(), t.Month()+1, 0, 0, 0, 0, 0, time.UTC).Day()
+		end      = time.Date(t.Year(), t.Month(), finalDay, 23, 59, 59, maxNsec, time.UTC)
+	)
+
+	return Period{Begin: begin, End: end}
+}
+
+func PreviousMonthOf(t time.Time) Period {
+	return MonthOf(t.AddDate(0, -1, 0))
+}
+
+func (p Period) Within(o Period) bool {
+	return (p.Begin.Equal(o.Begin) || p.Begin.After(o.Begin)) &&
+		(p.End.Equal(o.End) || p.End.Before(o.End))
+}
diff --git a/datetime/period_test.go b/datetime/period_test.go
new file mode 100644
index 0000000..b7e81a0
--- /dev/null
+++ b/datetime/period_test.go
@@ -0,0 +1,47 @@
+package datetime_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/blue-health/blue-go-toolbox/datetime"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPreviousMonthOf(t *testing.T) {
+	testCases := []struct {
+		in  time.Time
+		out datetime.Period
+	}{
+		{in: time.Date(2022, time.July, 1, 0, 0, 0, 0, time.UTC), out: datetime.Period{
+			Begin: time.Date(2022, time.June, 1, 0, 0, 0, 0, time.UTC),
+			End:   time.Date(2022, time.June, 30, 23, 59, 59, 999999999, time.UTC),
+		}},
+		{in: time.Date(2022, time.August, 1, 0, 0, 0, 0, time.UTC), out: datetime.Period{
+			Begin: time.Date(2022, time.July, 1, 0, 0, 0, 0, time.UTC),
+			End:   time.Date(2022, time.July, 31, 23, 59, 59, 999999999, time.UTC),
+		}},
+		{in: time.Date(2022, time.September, 3, 0, 0, 0, 0, time.UTC), out: datetime.Period{
+			Begin: time.Date(2022, time.August, 1, 0, 0, 0, 0, time.UTC),
+			End:   time.Date(2022, time.August, 31, 23, 59, 59, 999999999, time.UTC),
+		}},
+		{in: time.Date(2022, time.September, 15, 0, 0, 0, 0, time.UTC), out: datetime.Period{
+			Begin: time.Date(2022, time.August, 1, 0, 0, 0, 0, time.UTC),
+			End:   time.Date(2022, time.August, 31, 23, 59, 59, 999999999, time.UTC),
+		}},
+		{in: time.Date(2022, time.September, 30, 0, 0, 0, 0, time.UTC), out: datetime.Period{
+			Begin: time.Date(2022, time.August, 1, 0, 0, 0, 0, time.UTC),
+			End:   time.Date(2022, time.August, 31, 23, 59, 59, 999999999, time.UTC),
+		}},
+		{in: time.Date(2023, time.January, 1, 0, 0, 0, 0, time.UTC), out: datetime.Period{
+			Begin: time.Date(2022, time.December, 1, 0, 0, 0, 0, time.UTC),
+			End:   time.Date(2022, time.December, 31, 23, 59, 59, 999999999, time.UTC),
+		}},
+	}
+
+	for _, c := range testCases {
+		t.Run(c.in.Format(time.RFC1123), func(t *testing.T) {
+			require.Equal(t, c.out, datetime.PreviousMonthOf(c.in))
+		})
+	}
+}
diff --git a/datetime/time.go b/datetime/time.go
deleted file mode 100644
index 63ad5da..0000000
--- a/datetime/time.go
+++ /dev/null
@@ -1,25 +0,0 @@
-package datetime
-
-import "time"
-
-type Period struct {
-	Begin, End time.Time
-}
-
-func StartOfDay(t time.Time) time.Time {
-	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, time.UTC)
-}
-
-func EndOfDay(t time.Time) time.Time {
-	return time.Date(t.Year(), t.Month(), t.Day(), 23, 59, 59, 0, time.UTC)
-}
-
-func MonthOf(t time.Time) Period {
-	var (
-		begin    = time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, time.UTC)
-		finalDay = time.Date(t.Year(), t.Month()+1, 0, 0, 0, 0, 0, time.UTC).Day()
-		end      = time.Date(t.Year(), t.Month(), finalDay, 23, 59, 59, 0, time.UTC)
-	)
-
-	return Period{Begin: begin, End: end}
-}
diff --git a/go.mod b/go.mod
index a25aaf8..3ade9bc 100644
--- a/go.mod
+++ b/go.mod
@@ -16,7 +16,7 @@ require (
 	github.com/microcosm-cc/bluemonday v1.0.20
 	github.com/stretchr/testify v1.8.0
 	golang.org/x/crypto v0.0.0-20220829220503-c86fa9a7ed90
-	google.golang.org/genproto v0.0.0-20220909194730-69f6226f97e5
+	google.golang.org/genproto v0.0.0-20220914142337-ca0e39ece12f
 	gopkg.in/guregu/null.v4 v4.0.0
 	gopkg.in/yaml.v3 v3.0.1
 )
@@ -48,7 +48,7 @@ require (
 	golang.org/x/net v0.0.0-20220909164309-bea034e7d591 // indirect
 	golang.org/x/oauth2 v0.0.0-20220909003341-f21342109be1 // indirect
 	golang.org/x/sync v0.0.0-20220907140024-f12130a52804 // indirect
-	golang.org/x/sys v0.0.0-20220909162455-aba9fc2a8ff2 // indirect
+	golang.org/x/sys v0.0.0-20220913175220-63ea55921009 // indirect
 	golang.org/x/text v0.3.7 // indirect
 	google.golang.org/api v0.95.0 // indirect
 	google.golang.org/appengine v1.6.7 // indirect
diff --git a/go.sum b/go.sum
index d217126..f768e44 100644
--- a/go.sum
+++ b/go.sum
@@ -476,8 +476,8 @@ golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20220610221304-9f5ed59c137d/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220615213510-4f61da869c0c/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220624220833-87e55d714810/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220909162455-aba9fc2a8ff2 h1:wM1k/lXfpc5HdkJJyW9GELpd8ERGdnh8sMGL6Gzq3Ho=
-golang.org/x/sys v0.0.0-20220909162455-aba9fc2a8ff2/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220913175220-63ea55921009 h1:PuvuRMeLWqsf/ZdT1UUZz0syhioyv1mzuFZsXs4fvhw=
+golang.org/x/sys v0.0.0-20220913175220-63ea55921009/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
 golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
@@ -681,8 +681,8 @@ google.golang.org/genproto v0.0.0-20220608133413-ed9918b62aac/go.mod h1:KEWEmljW
 google.golang.org/genproto v0.0.0-20220616135557-88e70c0c3a90/go.mod h1:KEWEmljWE5zPzLBa/oHl6DaEt9LmfH6WtH1OHIvleBA=
 google.golang.org/genproto v0.0.0-20220617124728-180714bec0ad/go.mod h1:KEWEmljWE5zPzLBa/oHl6DaEt9LmfH6WtH1OHIvleBA=
 google.golang.org/genproto v0.0.0-20220624142145-8cd45d7dbd1f/go.mod h1:KEWEmljWE5zPzLBa/oHl6DaEt9LmfH6WtH1OHIvleBA=
-google.golang.org/genproto v0.0.0-20220909194730-69f6226f97e5 h1:ngtP8S8JkBWfJACT9cmj5eTkS9tIWPQI5leBz/7Bq/c=
-google.golang.org/genproto v0.0.0-20220909194730-69f6226f97e5/go.mod h1:0Nb8Qy+Sk5eDzHnzlStwW3itdNaWoZA5XeSG+R3JHSo=
+google.golang.org/genproto v0.0.0-20220914142337-ca0e39ece12f h1:wwbo0UziciPT4Dsca+bmplW53QNAl7tiUOw7FfAcsf8=
+google.golang.org/genproto v0.0.0-20220914142337-ca0e39ece12f/go.mod h1:0Nb8Qy+Sk5eDzHnzlStwW3itdNaWoZA5XeSG+R3JHSo=
 google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZiDr8c=
 google.golang.org/grpc v1.20.1/go.mod h1:10oTOabMzJvdu6/UiuZezV6QK5dSlG84ov/aaiqXj38=
 google.golang.org/grpc v1.21.1/go.mod h1:oYelfM1adQP15Ek0mdvEgi9Df8B9CZIaU1084ijfRaM=