Reclining a seat is a question of crew instructions, aircraft equipment and consideration for the person behind you. There is no universal passenger rule that reclining becomes acceptable at a particular cruising altitude.
Follow the crew’s directions
Put the seat in the required position whenever the crew instructs you, including preparation for takeoff and landing. Some seats do not recline or have a different control; do not force a mechanism that seems stuck.
Look before moving
When reclining is permitted, move slowly and check what is behind you. The other passenger may have a laptop open, a drink on the tray or limited space to adjust. A brief warning can prevent an avoidable spill or disagreement.
Consider meal service and shared space
If a meal is being served, returning the seat toward upright can make the tray easier to use behind you. The airline or crew may give specific directions. Seat pitch and recline vary, so use the actual space in front of you rather than assuming every cabin feels the same.
Handle disagreements calmly
If another passenger asks for a change, discuss a workable position politely. Avoid pushing a seat, blocking its movement or treating a comfort preference as a safety rule. Ask a crew member for help if the disagreement continues.
Choose a seat with your priorities in mind when options are available: a fixed-back seat, bulkhead or extra-legroom product can have different tradeoffs. Check the airline’s seat information before paying for a particular feature.