Please be aware that Yogyakarta has multiple airports and that these results are for all airports serving the city.
The best month to fly between Yogyakarta and Singapore is August and the most expensive month to fly is June. (Average prices, based on 1394 datapoints.)
The best day to arrive at Yogyakarta is Friday and it would be best to avoid Tuesday, as prices are on average 114.9% higher than on Friday. (Average prices, based on 541 datapoints.)