It’s free and has no adverts but there are two problems. With newer iPhones the app stays running in the background and only updates the days until figure when it’s killed/restarted. So you’ll get the same days until figure for a whole week. Additionally it displays the wrong days until figure - today is Friday and my date is set for Sunday but it displays 1 day to go when it should be 2. This may be a time zone issue?