// Your moment

var mmt = moment();



// Your moment at midnight

var mmtMidnight = mmt.clone().startOf('day');



// Difference in minutes

var diffMinutes = mmt.diff(mmtMidnight, 'minutes');

By default, moment#diff will return number rounded down. If you want the floating point number, pass true as the third argument. Before 2.0.0, moment#diff returned rounded number, not a rounded down number.

Consider this pseudocode because I haven't test to see if the difference takes into account DST.