Do wedding invitations need extra postage in the UK?

In the UK, postage is based on size and weight, not on the fact that it is a wedding invitation. A standard invitation that fits within the Royal Mail's letter size limits (up to 240mm by 165mm, up to 5mm thick, and up to 100g) needs only a normal first or second class stamp. However, many wedding invitations are heavier or larger because of thick card, multiple layers, or decorative additions like ribbons, wax seals or pocketfold envelopes. Those will need a 'large letter' stamp, which costs more. If your invitation is very heavy or bulky, it could even go into the small parcel rate. To avoid extra postage, keep your design simple and flat. Weigh your completed invitation at the post office before you buy stamps. If you are sending invitations abroad, international postage rates apply and will be higher than domestic rates. Also, if you add a reply card with a pre-paid envelope, that envelope needs its own stamp, but that is separate from the invitation postage. Always check the current Royal Mail size and weight guidelines, as they can change.