You may log in to your Singpass to retrieve your marriage date which is found under 'Family' of 'My Profile'. 

Alternatively, you may click here to conduct a search for marriage record to locate the marriage date. Singapore Citizens and Permanent Residents holding Singpass can enjoy up to two free online searches over a period of 12 months from the date of the first search. This free service will only provide online display of the search results. 

If you have a digital copy of your marriage certificate, you may refer to the said copy for your marriage date.