Subtracting days from a DateTime object in PowerShell

For those unfamiliar with DateTime objects, the problem is exceedingly simple – but the solution is even simpler.

Take the following DateTime object:

PS C:UsersAbrodie> $dt = get-date
PS C:UsersAbrodie> $dt

03 November 2011 17:48:56

If I look at the methods available, you can see there’s a conveniently long set of Add methods, enough to satisfy your every whim:

PS C:UsersAbrodie> $dt | Get-Member -MemberType Method | Format-Wide

Add                                                                             AddDays
AddHours                                                                        AddMilliseconds
AddMinutes                                                                      AddMonths
AddSeconds                                                                      AddTicks
Equals                                                                          GetDateTimeFormats
GetHashCode                                                                     GetType
GetTypeCode                                                                     IsDaylightSavingTime
Subtract                                                                        ToBinary
ToFileTime                                                                      ToFileTimeUtc
ToLocalTime                                                                     ToLongDateString
ToLongTimeString                                                                ToOADate
ToShortDateString                                                               ToShortTimeString
ToString                                                                        ToUniversalTime

All those lovely Add* methods, but only one subtract, which takes a TimeSpan object.

I found the following very useful blog entry on, which details how to construct a TimeSpan instance and pass it to the Subtract method.

However, easiest way to perform a subtraction is simply to use arithmetic logic.  I.e.

PS C:UsersAbrodie> $dt.AddDays(-1)

02 November 2011 17:48:56

If you heard a slight cracking sound, as if a hand slapped a forehead quite hard, around 7:23am on Thursday 3rd November, that was me!

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