PIA, Air India and Saudia all have different standard checked baggage allowances to British Airways or Emirates on the same general route, and family-visit travellers carrying gifts or shopping routinely exceed whichever allowance applies. Check your specific airline's allowance at the time of booking rather than assuming "international flight" means a standard 23kg, and pre-purchase extra baggage online rather than paying the airport rate.
Allowances also vary within a single airline, by fare type, cabin and sometimes by route, so check the allowance printed on your actual booking, not a figure remembered from a previous trip. Weigh bags at home before leaving for the airport. The check-in desk is the most expensive place in the journey to discover you're three kilos over. And don't ignore hand baggage: weight limits on it are enforced far more strictly at some overseas airports than they typically are in the UK.
The leg that catches people out is the return. The flight out is usually packed with intention; the flight home carries everything accumulated across weeks of family visits, shopping and gifts. If you know from experience the return always runs heavy, pre-buying extra allowance for the return leg only, at the online rate, before you fly home, is consistently cheaper than negotiating at an airport desk on departure day.