July 2024 Postage Rates For Large Envelopes. All postcards and envelopes (or flats) must be rectangular, otherwise an additional charge may apply.  — the baseline postage rate to mail a flat/large envelope has increased from $1.35 to $1.39 in postage, but the price for each additional ounce also stayed the same.

The usps introduced two rate changes in july. Postal service filed notice with the postal regulatory commission of mailing services price changes to take effect july 14,.