Sex activity during Ramadan:
Sex activity during the day in Ramadaan is haraam for men and women alike, who are obliged to fast during the day. Doing that is a sin for which expiation (kafaarah) must be offered. The kafaarah is to free a slave; if that is not possible then the person must fast for two consecutive months; whoever is not able to do that must feed sixty poor persons.
It was narrated that Abu Hurayrah (may Allah be pleased with him) said: Whilst we were sitting with the Prophet (peace and blessings of Allah be upon him), a man came to him and said, “O Messenger of Allaah, I am doomed!” He said, “What happened?” He said, “I had intercourse with my wife when I was fasting [in Ramadan].” The Messenger of Allah (peace and blessings of Allah be upon him) said, “Are you able to free a slave?” He said, “No.” He said, “Are you able to fast for two consecutive months?” He said, “No.” He said, “Can you feed sixty poor persons?” He said, “No.” Then the Prophet (peace and blessings of Allah be upon him) remained silent for a while, and whilst we were like that, a large vessel of dates was brought to the Prophet (peace and blessings of Allah be upon him), and he said, “Where is the one who was asking?” He said, “Here I am.” He said, “Take these and give them in charity.” The man said, “Is there anyone more poor than me, O Messenger of Allah? For there is no household between the two harrahs (lava fields – i.e., in Madeenah) that is poorer than my household.” The Messenger of Allah (peace and blessings of Allah be upon him) smiled until his eyeteeth could be seen, then he said, “Feed it to your family.” (Narrated by al-Bukhaari, 1834, 1835; Muslim, 1111)
With regard to intercourse during the night in Ramadan, this is permitted and is not forbidden, and the time when it is permitted lasts until the onset of dawn. When dawn comes, intercourse becomes forbidden.
Married Muslims can have sex after breaking the fast till seher i.e from sunset till sunrise. The ayat also defines the limit of eating in morning at dawn.
For Muslim married couple, Allah says in Quran (interpretation of the meaning):
“It is made lawful for you to have sexual relations with your wives on the night of As-Sawm (the fasts). They are Libaas [i.e. body-cover, or screen, or Sakan (i.e. you enjoy the pleasure of living with them] for you and you are the same for them. Allah knows that you used to deceive yourselves, so He turned to you (accepted your repentance) and forgave you. So now have sexual relations with them and seek that which Allah has ordained for you (offspring), and eat and drink until the white thread (light) of dawn appears to you distinct from the black thread (darkness of night), then complete your Sawm (fast) till the nightfall” (Al-Baqarah 2:187)
You can read also: Ramadan 2020: Festival of Ramadan and the purpose of Ramadan.
You can read also: What happened in Ramadan and Why is it so important for Muslims?
You can read also: What is the Laylat al-Qadr and how to prepare for Laylat al-Qadr in Ramadan?
This verse clearly states that it is permissible to eat, drink and have intercourse during the nights of Ramadan until dawn. After having intercourse, it is obligatory to do ghusl (bathing), then pray Fajr. Source: Islam Info
If not fasting during Ramadan:
If you are not fasting then there should be an Islamic reason to skip the fasting. You should be weak enough or have a bad fever or you are travelling to long distance.In all these reasons man is not able to do sex. if you skip the fasting with no reason then you will be punished by Allah and if your reason to skip fasting is Islamic then there is no chance to have sex.