Treasure Chest (BTD5 and BTD6)

"... Speaking of Monkey Money, for those more awesome fans that log in everyday, now you'll earn 2x, 3x, 4x or even 5x from the Daily Rewards Chest for logging in multiple times in a row. Logging in 7+ times in a row earns 5x Daily Rewards, which is up to 100 just for logging in!"

- Part of a quote from the July 12th 2012 update.

Bloons TD 5
On Jan 19, 2012, an update occurred for Bloons Tower Defense 5 that added a Treasure Chest (Money Chest in Bloons TD 5 Mobile) on the main screen in the game. The treasure chest can also be found in Bloons TD 5 Deluxe and Bloons TD 5 Mobile. The player can click the treasure chest once a day. On Flash, it gives the player some free Monkey Money every day. Since update on Jul 12, 2012, the amount of Monkey Money is usually between $10 and $20 (used to be between $9 and $15) and logging in 2 days in a row earns 2&times; daily rewards, 3 & 4 days in a row earns 3&times;, 5 & 6 days in a row earns 4&times;, and 7+ days in a row earns 5&times; daily rewards. The Money Chest resets at midnight (0:00 or 12:00 a.m.) (GMT/UTC) on the web version. Upon opening the chest, a white text will pop up that says "COME BACK EVERYDAY!".

Bugs
If you play a game and the treasure chest updates while you are playing and you go back to the main screen, the treasure chest will be opened and you will see the chest is showing 999 with a stack of cash at the bottom. Clicking on the chest will give a player tomorrow's Monkey Money, but the player won't be able to open the chest the next day.

Also, occasionally a glitch will occur which causes the player to logout every time they try to open the chest. This is usually fixed by switching computers, and doing so will increase the number of days in a row by one.

Bloons TD 5 Mobile
On Bloons TD 5 Mobile, as of July 29, 2016, the chest gives a wide variety of rewards, including double Monkey Money (provided for 3 days), free Towers, Special Agents, Tokens, and Monkey Money. When the chest is opened, rewards are shown for the next 4 days, as well as what was earned on the current day. Rewards are stated in the following chart:

 When the day 60 is reached, rewards repeat from day 30 (60 = 30, 61 = 31, 62 = 32, etc.)

Bloons TD 6
In BTD6, the Treasure Chest has been released ever since the game's beta release to the top YouTubers of Bloons TD, a few days before the official release. On version 11.0, the entire Treasure Chest system was modified entirely to include random Insta-Monkeys and also new types of rewards such as Energizing Totem and Tech Bot added after the game release. The system was reworked again on version 26.0 to include Race Pass added on version 24.0.

 When the day 51 is reached, rewards repeat from day 1 (51 = 1, 52 = 2, 53 = 3, etc.).

Trivia

 * Sometimes you can collect the next consecutive day's free Monkey Money by refreshing the game and then clicking on the treasure chest. This only depends if you play it after 24 hours from the previous day's free Monkey Money.
 * The player can collect their next day's Monkey Money after 00:00 UTC. Thus one can earn their daily Monkey Money at 23:55 UTC and then the next day's one at 00:05 UTC. However, this does not mean that one can repetitively collect Monkey Money within a short timeframe.