diff --git a/Data/Dates.hs b/Data/Dates.hs
--- a/Data/Dates.hs
+++ b/Data/Dates.hs
@@ -3,19 +3,31 @@
 module Data.Dates
   (DateTime (..),
    Time (..),
+   WeekDay (..),
    parseDate,
    pDate, pDateTime, pTime,
+   pDateInterval,
    getCurrentDateTime,
    tryRead,
    DateIntervalType (..),
    DateInterval (..),
-   addInterval, addTime
+   dayToDateTime, dateTimeToDay,
+   weekdayToInterval,
+   weekdayNumber,
+   intToWeekday,
+   dateWeekDay,
+   lastMonday, nextMonday,
+   modifyDate,
+   datesDifference,
+   addInterval, negateInterval, minusInterval,
+   addTime
   ) where
 
 import Prelude.Unicode
 import Data.Char (toUpper)
 import Data.List
 import Data.Time.Calendar
+import Data.Time.Calendar.WeekDate
 import Data.Time.LocalTime
 import Text.Parsec
 import Text.Parsec.String
@@ -24,6 +36,45 @@
 import Data.Dates.Types
 import Data.Dates.Internal
 
+data DateIntervalType = Day | Week | Month | Year
+  deriving (Eq,Show,Read,Data,Typeable)
+
+data DateInterval = Days ℤ
+                  | Weeks ℤ
+                  | Months ℤ
+                  | Years ℤ
+  deriving (Eq,Show,Data,Typeable)
+
+data WeekDay =
+    Monday
+  | Tuesday
+  | Wednesday
+  | Thursday
+  | Friday
+  | Saturday
+  | Sunday
+  deriving (Eq, Show, Read, Ord, Enum, Bounded, Data, Typeable)
+
+-- | Weekday as interval from Monday, so that
+-- weekdayToInterval Monday == 0 and
+-- weekdayToInterval Sunday == 6.
+weekdayToInterval ∷ WeekDay → DateInterval
+weekdayToInterval wd = Days (fromIntegral $ fromEnum wd)
+
+-- | Number of weekday, with Monday == 1 and Sunday == 7.
+weekdayNumber ∷ WeekDay → Int
+weekdayNumber wd = fromEnum wd + 1
+
+-- | Reverse for weekdayNumber
+intToWeekday ∷ Int → WeekDay
+intToWeekday i = toEnum (i - 1)
+
+lastMonday ∷ DateTime → DateTime
+lastMonday dt = dt `minusInterval` weekdayToInterval (dateWeekDay dt)
+
+nextMonday ∷ DateTime → DateTime
+nextMonday dt = lastMonday dt `addInterval` Weeks 1
+
 -- | Get current date and time.
 getCurrentDateTime ∷  IO DateTime
 getCurrentDateTime = do
@@ -37,6 +88,12 @@
       s = round $ todSec ltod
   return $ DateTime (fromIntegral y) m d h mins s
 
+-- | Get weekday of given date.
+dateWeekDay ∷ DateTime → WeekDay
+dateWeekDay dt =
+  let (_,_,wd) = toWeekDate (dateTimeToDay dt)
+  in  intToWeekday wd
+
 uppercase ∷ String → String
 uppercase = map toUpper
 
@@ -181,54 +238,130 @@
                           euroNumDate',
                           americanDate']
 
-data DateIntervalType = Day | Week | Month | Year
-  deriving (Eq,Show,Read)
-
-data DateInterval = Days ℤ
-                  | Weeks ℤ
-                  | Months ℤ
-                  | Years ℤ
-  deriving (Eq,Show)
-
-convertTo ∷  DateTime → Day
-convertTo dt = fromGregorian (fromIntegral $ year dt) (month dt) (day dt)
+-- | Convert date from DateTime to Day
+dateTimeToDay ∷  DateTime → Day
+dateTimeToDay dt = fromGregorian (fromIntegral $ year dt) (month dt) (day dt)
 
-convertFrom ∷  Day → DateTime
-convertFrom dt = 
+-- | Convert date from Day to DateTime
+dayToDateTime ∷  Day → DateTime
+dayToDateTime dt = 
   let (y,m,d) = toGregorian dt
   in  date (fromIntegral y) m d
 
+-- | Modify DateTime with pure function on Day
 modifyDate ∷  (t → Day → Day) → t → DateTime → DateTime
-modifyDate fn x dt = convertFrom $ fn x $ convertTo dt
+modifyDate fn x dt = dayToDateTime $ fn x $ dateTimeToDay dt
 
+-- | Add date interval to DateTime
 addInterval ∷  DateTime → DateInterval → DateTime
 addInterval dt (Days ds) = modifyDate addDays ds dt
 addInterval dt (Weeks ws) = modifyDate addDays (ws*7) dt
 addInterval dt (Months ms) = modifyDate addGregorianMonthsClip ms dt
 addInterval dt (Years ys) = modifyDate addGregorianYearsClip ys dt
 
+-- | Negate DateInterval value: Days 3 → Days (-3).
+negateInterval ∷ DateInterval → DateInterval
+negateInterval (Days n)   = Days (negate n)
+negateInterval (Weeks n)  = Weeks (negate n)
+negateInterval (Months n) = Months (negate n)
+negateInterval (Years n)  = Years (negate n)
+
+-- | Subtract DateInterval from DateTime.
+minusInterval ∷ DateTime → DateInterval → DateTime
+minusInterval date int = date `addInterval` negateInterval int
+
+-- | Number of days between two dates
+datesDifference ∷ DateTime → DateTime → Integer
+datesDifference d1 d2 =
+  abs $ toModifiedJulianDay (dateTimeToDay d1) -
+        toModifiedJulianDay (dateTimeToDay d2)
+
 maybePlural ∷ String → Parsec String st String
 maybePlural str = do
   r ← string str
   optional $ char 's'
   return (capitalize r)
 
-pDateInterval ∷ Parsec String st DateIntervalType
-pDateInterval = do
+pDateIntervalType ∷ Parsec String st DateIntervalType
+pDateIntervalType = do
   s ← choice $ map maybePlural ["day", "week", "month", "year"]
   tryRead s
 
+pDateInterval ∷ Parsec String st DateInterval
+pDateInterval = do
+  n ← many1 digit
+  spaces
+  tp ← pDateIntervalType
+  case tp of
+    Day →   Days   `fmap` tryRead n
+    Week →  Weeks  `fmap` tryRead n
+    Month → Months `fmap` tryRead n
+    Year →  Years  `fmap` tryRead n
+
 pRelDate ∷ DateTime → Parsec String st DateTime
 pRelDate date = do
-  offs ← (try futureDate) <|> (try passDate) <|> (try today) <|> (try tomorrow) <|> yesterday
+  offs ← try futureDate
+     <|> try passDate
+     <|> try today
+     <|> try tomorrow
+     <|> yesterday
   return $ date `addInterval` offs
 
+lastDate ∷ DateTime → Parsec String st DateTime
+lastDate now = do
+    string "last"
+    spaces
+    try byweek <|> try bymonth <|> byyear
+  where
+    byweek = do
+      wd ← try (string "week" >> return Monday) <|> pWeekDay
+      let monday = lastMonday now
+          monday' = if wd > dateWeekDay now
+                      then monday `minusInterval` Weeks 1
+                      else monday
+      return $ monday' `addInterval` weekdayToInterval wd
+
+    bymonth = do
+      string "month"
+      return $ now {day = 1}
+
+    byyear = do
+      string "year"
+      return $ now {month = 1, day = 1}
+
+nextDate ∷ DateTime → Parsec String st DateTime
+nextDate now = do
+    string "next"
+    spaces
+    try byweek <|> try bymonth <|> byyear
+  where
+    byweek = do
+      wd ← try (string "week" >> return Monday) <|> pWeekDay
+      let monday = nextMonday now
+          monday' = if wd > dateWeekDay now
+                      then monday `minusInterval` Weeks 1
+                      else monday
+      return $ monday' `addInterval` weekdayToInterval wd
+
+    bymonth = do
+      string "month"
+      return (now `addInterval` Months 1) {day = 1}
+
+    byyear = do
+      string "year"
+      return (now `addInterval` Years 1) {month = 1, day = 1}
+
+pWeekDay ∷ Parsec String st WeekDay
+pWeekDay = do
+  w ← many1 (oneOf "mondaytueswnhrfi")
+  tryRead (capitalize w)
+
 futureDate ∷ Parsec String st DateInterval
 futureDate = do
   string "in "
   n ← many1 digit
   char ' '
-  tp ← pDateInterval
+  tp ← pDateIntervalType
   case tp of
     Day →   Days   `fmap` tryRead n
     Week →  Weeks  `fmap` tryRead n
@@ -239,7 +372,7 @@
 passDate = do
   n ← many1 digit
   char ' '
-  tp ← pDateInterval
+  tp ← pDateIntervalType
   string " ago"
   case tp of
     Day →   (Days   . negate) `fmap` tryRead n
@@ -249,7 +382,7 @@
 
 today ∷ Parsec String st DateInterval
 today = do
-  string "today"
+  string "today" <|> string "now"
   return $ Days 0
 
 tomorrow ∷ Parsec String st DateInterval
@@ -262,15 +395,25 @@
   string "yesterday"
   return $ Days (-1)
 
+pByWeek ∷ DateTime → Parsec String st DateTime
+pByWeek date =
+  try (lastDate date) <|> nextDate date
+
 -- | Parsec parser for DateTime.
 pDateTime ∷ DateTime       -- ^ Current date / time, to use as base for relative dates
           → Parsec String st DateTime
-pDateTime date =  (try $ pRelDate date) <|> (try $ pAbsDateTime $ year date)
+pDateTime date =
+      (try $ pRelDate date)
+  <|> (try $ pByWeek date)
+  <|> (try $ pAbsDateTime $ year date)
 
 -- | Parsec parser for Date only.
 pDate ∷ DateTime       -- ^ Current date / time, to use as base for relative dates
           → Parsec String st DateTime
-pDate date =  (try $ pRelDate date) <|> (try $ pAbsDate $ year date)
+pDate date =
+      (try $ pRelDate date)
+  <|> (try $ pByWeek date)
+  <|> (try $ pAbsDate $ year date)
 
 -- | Parse date/time
 parseDate ∷ DateTime  -- ^ Current date / time, to use as base for relative dates
diff --git a/dates.cabal b/dates.cabal
--- a/dates.cabal
+++ b/dates.cabal
@@ -1,5 +1,5 @@
 name:                dates
-version:             0.2.0.2
+version:             0.2.1.0
 synopsis:            Small library for parsing different dates formats.
 description:         This package allows to parse many different formats
                      of dates. Both absolute and relative dates are supported.
@@ -14,6 +14,10 @@
                        * `today', `tomorrow', `yesterday'
                        .
                        * `in 2 days', '3 weeks ago'
+                       .
+                       * `last monday', 'next friday'
+                       .
+                       * `last month' (1th of this month), `next year' (1th of January of next year)
                      .
                      4-digits years may be abbreviated (such as 12 for 2012).
                      Both 12-hour and 24-hour time formats are supported.
@@ -37,9 +41,9 @@
                        Data.Dates.Formats,
                        Data.Dates.Internal
   -- other-modules:       
-  build-depends:       base ==4.5.*,
+  build-depends:       base >=4 && < 5,
                        base-unicode-symbols ==0.2.*,
-                       time ==1.4.*,
+                       time >= 1.4,
                        parsec ==3.1.*,
                        syb ==0.3.*