X0306 4 2017-09-11 0 0001082923 STAMPS.COM INC STMP 0001334644 Biswas Michael John 1990 E. GRAND AVE. EL SEGUNDO CA 90245 0 1 0 0 Chief Technology Officer Common Stock 2017-09-11 4 M 0 13468 12.55 A 15365 D Common Stock 2017-09-11 4 M 0 24032 32.41 A 39397 D Common Stock 2017-09-11 4 S 0 9057 190.2446 D 30340 D Common Stock 2017-09-11 4 S 0 3609 191.0469 D 26731 D Common Stock 2017-09-11 4 S 0 10841 192.2951 D 15890 D Common Stock 2017-09-11 4 S 0 13226 193.0648 D 2664 D Common Stock 2017-09-11 4 S 0 2050 193.9244 D 614 D Common Stock 2017-09-11 4 S 0 319 194.9238 D 295 D Common Stock 2017-09-13 4 M 0 37500 32.41 A 37795 D Common Stock 2017-09-13 4 S 0 15382 200.1596 D 22413 D Common Stock 2017-09-13 4 S 0 10428 201.6838 D 11985 D Common Stock 2017-09-13 4 S 0 11440 202.1965 D 545 D Common Stock 2017-09-13 4 S 0 250 203.15 D 295 D Stock Option (Common Stock) 12.55 2017-09-11 4 M 0 11476 0.00 D 2011-05-20 2021-05-20 Common Stock 13468 215976 D Stock Option (Common Stock) 32.41 2017-09-11 4 M 0 24032 0.00 D 2015-10-19 2024-09-19 Common Stock 24032 191944 D Stock Options(Common Stock) 32.41 2017-09-13 4 M 0 37500 0.00 D 2015-10-19 2024-09-19 Common Stock 37500 154444 D This sale was executed pursuant to a prearranged trading plan compliant with Rule 10b5-1. This sale price reflects a weighted average of multiple prices ranging from $189.70 to $190.65. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $190.70 to $191.60. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $191.70 to $192.65. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $192.70 to $193.65. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $193.70 to $194.30. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $194.90 to $195.30. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $200.00 to $200.95. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $201.15 to $201.925. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. This sale price reflects a weighted average of multiple prices ranging from $201.95 to $202.70. Full information regarding the number of shares sold at each price will be provided to the Securities and Exchange Commission staff, the issuer or any security holder, upon request. /s/ Matthew A. Lipson, by Power of Attorney for Michael Biswas 2017-09-13