datefix

Version 1.0.0 | 2026-04-08

datefix converts string date variables to numeric Stata daily dates and applies a daily-date display format. It is designed for the common cleanup step after import, especially when date order is inconsistent, two-digit years need disambiguation, or you want to preserve the original string alongside a cleaned numeric date.

Requirements

• Stata 16 or later

Installation

capture ado uninstall datefix
net install datefix, from("https://raw.githubusercontent.com/tpcopeland/Stata-Tools/main/datefix") replace

Commands

Command	Description
datefix	Convert one or more string date variables to numeric Stata daily dates, optionally into a new variable with a custom display format

Quick Start

If the imported dates are unambiguous, datefix can usually infer the correct ordering and replace the original string variable in place.

clear
input str10 visit_date
"31/01/2020"
"15/02/2020"
"07/03/2020"
end

datefix visit_date
list

In this example, datefix will auto-detect the ordering that produces the most valid parses, convert visit_date to a numeric daily date, and apply the default %tdCCYY/NN/DD format.

How It Works

• Without newvar(), each variable in varlist is converted in place.
• With newvar(), only one source variable may be specified, and the original variable is preserved unless drop is also requested.
• If order() is omitted, datefix tests MDY, DMY, and YMD and uses the ordering that produces the most valid parses. If the strings are ambiguous, specify order() explicitly.
• topyear() passes Stata's topyear argument to date() so two-digit years are interpreted correctly.
• If a variable is already numeric, datefix can still copy it to newvar() and apply a different daily-date display format.

Worked Examples

1. Auto-detect the ordering and replace the original variables

This is the default cleanup workflow for imported string dates.

clear
input str10 dob str10 dod
"31/01/2020" "02/02/2020"
"15/02/2020" "18/02/2020"
end

datefix dob dod
list

2. Preserve the original string and write a new formatted date variable

Use newvar() when you want to keep the raw imported string alongside the cleaned Stata date.

clear
input str10 visit_date
"03/14/2020"
"04/20/2020"
"05/01/2020"
end

datefix visit_date, newvar(vdate) order(MDY) df(%tdMonth_DD,_CCYY)
list

3. Handle two-digit years explicitly

When the source data use two-digit years, topyear() tells Stata how those years should be interpreted.

clear
input str8 founded
"07/04/76"
"11/12/84"
"05/09/91"
end

datefix founded, order(MDY) topyear(1900)
list

4. Copy an already numeric date variable and change only the display format

datefix also works as a lightweight formatting helper when the dates are already numeric Stata daily dates.

clear
input double visit_num
21915
21945
21988
end
format %td visit_num

datefix visit_num, newvar(visit_label) df(%tdDD_Mon._CCYY)
list

Common df() Formats

Format string	Example output	Use
%tdCCYY/NN/DD	2020/01/10	Default year-month-day display
%tdDD/NN/CCYY	10/01/2020	Day-month-year display
%tdMonth_DD,_CCYY	January 10, 2020	Full month name
%tdDD_Mon._CCYY	10 Jan. 2020	Compact manuscript-style date

For the full set of Stata date display formats, see help datetime_display_formats.

Practical Notes

• newvar() cannot be combined with multiple source variables.
• drop is only meaningful when newvar() is used.
• datefix stops when it encounters strings with : because those look like datetimes rather than daily dates.
• Missing-value counts are reported before and after conversion so you can spot parsing problems quickly.
• datefix does not store results in r().

Version History

• 1.0.0 (2026-04-08): Initial release with auto-detection, newvar(), custom display formats, and topyear() support.

Author

Timothy P Copeland, Karolinska Institutet