How to Set Date and Time Format in IIS Manager

A common point of confusion when people search for how to 'set the date format in IIS' is that IIS Manager itself doesn't actually control date and time formatting for your application's output at all — IIS is a web server that hosts and routes requests to your application; how dates get formatted when your application renders them is determined by your application's own code and configuration, not by anything in the IIS Manager UI.

What actually controls date formatting for an ASP.NET application running under IIS is the application's culture and region settings, which flow from either the .NET globalization configuration or explicit formatting calls in your code — this is the layer worth focusing on, rather than searching through IIS Manager's interface for a setting that doesn't exist there.

In a .NET application, the most direct fix is being explicit about culture wherever you format a date rather than relying on server defaults, which can vary between machines and even change after a server-level Windows update. Using DateTime.ToString() with an explicit format string and CultureInfo — for example, myDate.ToString('dd/MM/yyyy', CultureInfo.InvariantCulture) — guarantees consistent output regardless of what the underlying server's regional settings happen to be.

If the goal is genuinely to change the server's regional settings, that's controlled through Windows itself — Region settings in Windows Server's Control Panel — rather than through IIS Manager, since IIS runs application pools using the underlying operating system's configured culture unless the application explicitly overrides it. Changing this affects every application on the server, though, which is usually not what you actually want if only one application needs a specific date format.

For ASP.NET Core specifically, you can also set the default culture at the application level in Program.cs using the app's localization configuration, which takes effect for that application regardless of the underlying server's regional settings — this is generally the more maintainable approach for a deployed application, since it travels with your code rather than depending on manual server configuration that's easy to forget when provisioning a new server or deploying to a new environment.

If you're troubleshooting dates that display correctly on your local development machine but incorrectly once deployed to IIS, the server's culture settings differing from your local machine's are the most likely explanation — explicitly specifying the culture in your formatting code, rather than depending on whatever culture the hosting environment happens to default to, is the fix that travels reliably across every environment your application runs in.