The Iron Bank is a remodeling of "agot mechanism expansion" by sharpforever available on Steam Workshop. It adds a banking system that allows you to deposit gold, interest is paid every three years, take loans, and allows the bank to retaliate on failure to pay. Interest in "agot mechanism expansion" paid the money to your treasury, this one reinvests the interest back into bank account, and it can be withdrawn from the Iron Bank GUI which is added to HUD. It doesn't require A Game of Thrones, sharpforever's, or IsaBeau's mods to work. It does require a new game save to work.

Updated: 2.0
Now includes remodeled mechanics from "Better Banking"  by IsaBeau available on Steam Workshop. The Start Banking System decision which currently in "Better Banking" does nothing, now requires a 40,000 gold deposit, which will accrue a 3% yearly interest rate, with 17 gold being added to your treasury each month and the remainder being added to your account at the Iron Bank.

Your initial deposit of 40,000 can be refunded by a decision to end your participation in the banking system, but does not show and is not accessible in your Iron Bank account funds.

Additionally, using mechanics found in Better Banking, which allows for war bonds and the banking system to be passed from one character to their heir when they die, the Iron Bank will now transfer the account balance of your current ruler when they die to a bank account with their heir. If the heir already has a bank account, the balance will be added to the existing account.

Updated: 2.1
I noticed an issue with the functioning of the better banking mechanics, the fact that AI customers had their funds reinvested into their accounts which would cause them to close their accounts, along with the fact that the banker themselves kept having their gold go in the negative. All seems to be working now. Hopefully, this will be the last update. If you began a game with the mod loaded, it can be updated mid-playthrough, a new game is required for the initialization to happen.

Updated: 2.2
Okay, as anyone who tried the mod up until now will have likely noticed some flaws in how it was running, this should hopefully be the last attempt needed to fix that. Having done a few run-throughs now, it seems to be acting appropriately all around.

Opening banking system can only be used once, it no longer provides monthly income, it now accurately provides a 3% return on investment a year placed into your bank account. Bank accounts and banking systems should pass on to new heirs. The Iron Bank will no longer wildly fluctuate how much cash it has, and will instead have the slow and steady profit margin it is meant to have. The AI characters should be having their money sent directly to them, and the player's reinvested into the bank account.

Hopefully, there isn't anything I missed, or, messed up.

Addendum: Messed up and originally loaded the 2.2 version with an outdated decision file that allowed Banking System to be selected more than once. Corrected. Mod version is not updated, the 2.2 files were replaced with the corrected version.

Updated: 2.2a
Updated to include the new option of investing in stocks, which is available through character interaction in the diplomacy menu with the Keyholder of the Iron Bank. Stocks, when valued over 10,000, will produce random returns each year ranging from 17% to a one-in-ten chance of losing 10% of your stock value. Your stock values are shown on the Iron Bank window, beneath your bank account balance. Stocks, when valued below 10,000, will return a set 10%, minus a 1% fee to the bank (IE, you get 9% of the value, Keyholder gets 1% of the value). This mimics the realism of certain financial accounts having guaranteed returns up to a certain point and prevents stocks from going into the negative (as I don't really yet have the skill to program an appropriate response to this, IE, calling in debt on margin loans).

Bank account has been maxed at 6,000,000; which is unlikely to be reached, but if it is, interest from the bank account will instead be "invested" (added) to stocks, which are also maxed at 6,000,000; which is again unlikely to be reached. Allowing a character to reach a total of 12,000,000 invested with the Iron Bank.

Deposits, withdrawals, and interest on the account now include fees paid to the Iron Bank, ranging from 10% and reducing down to low as 5% depending on the amounts. This is done for realism, to aid in the Iron Bank actually maintaining long-term positive cash, and to lessen the overpowered nature of the banking system, which will now require a year to break even, two to break even on withdrawals, and three or more to actually turn a profit that you can access.

Sets a maximum gold budget for the Keyholder of the Iron Bank, to prevent the possibility of their values going so high as to exceed the game's ability to count, and go into the negative.

Sets a variable that will have the AI withdraw all cash if at war and their accounts have more gold than their treasury does that year, if not at war there is a chance they will withdraw a portion of their account that year.

Note: Updating from the previous version doesn't require a new game.

Updated: 2.3

Updated to expand on the amounts that are available to be used as loans, and to increase the penalty of defaulting on loans by providing a decision that allows those waging proxy wars for the Iron Bank to summon mercenaries from the Iron Bank, making it more difficult.

Note: First version contained a coding error preventing deposits, it’s been corrected.

Updated: 3.1

Updated to change the “stocks” option of the Iron Bank to “investment”, and to add a proper stock market including buying stocks in the production of the following goods:
Grain (cheap stock),
Sugar,
Walnuts,
Chestnuts,
Cherries,
Strawberries,
Garlic,
Potatoes (cheap stock),
Lemons,
Oranges,
Pomegranates,
Figs,
Apples,
Pears,
Peaches,
Plums,
Grapes,
Wine,
Aged Wine,
Fortified Wine,
Spiced Wine,
Fortified Aged Wine,
Spiced Aged Wine,
Fortified-Spiced Aged Wine (most expensive stock),
Salt,
Pepper,
Cinnamon,
Ginger,
Saffron,
Nutmeg,
Mace,
Cloves,
Frankincense,
Amchoor,
Harad,
Kabra,
Jeera,
Sarson,
Laung,
Agarwood.

Each year each of these stocks changes according to one of fifty available options, ranging from 11% increase to a -10% decrease, along with a chance for stocks to split, decreasing the stock’s value by half but doubling the number of stocks you may own. Stocks can be bought, and sold, in quantities of: one, ten, fifty, and one hundred. Stocks and their quantities only appear if you can afford to buy or have that quantity available to sell. The number and value of stocks owned is inherited. Stocks have no fees to buy, but do have a 10% fee to sell. They have an 18% chance pf losing value every year, a 2% chance of splitting, and a 80% chance of gaining value. Most increases are not even 1% increments, with a 4% chance of gaining more than 10% in value a year. These odds change depending on how much the stock is worth, they can only loose so much, and after gaining so much the chance of a loss increases. They are designed to be a longer term investment than deposits and the investment, likely taking an in game decade or longer to be viable for profit, but not necessarily that long, and of course, the possibility of a loss.

It will give you two traits:

Portfolio: The number of stocks you own.

The Stock Market: The current price of the stocks available.

It shouldn’t require a new game to be used.

Note: Updated to include maximum number of stocks allowed to be owned, thereby giving additional utility to stocks splitting. Interface messages added to make the player aware if a stock splits.

Note II: Updated to correct issues that seemed to arise from implementing both the stock market and the banking system. Now the stock numbers, valued, bank deposits, and investments provide interest again and do properly inherit from one character to the next.

Note III: Updated to correct an issue from testing causing grain stocks to split every year.

Note IV: Updated to correct an error that was allowing AI characters to sell stocks they didn’t own and spam free gold. Unless any further errors need correcting, this may be the final version of The Iron Bank.

Note V: Update to correct and error with an AI decision.

Note VI: Update in another attempt to correct splitting of stocks happening too often.

Update: 4.1

Along with attempting to correct remaining issues with current coding, is update 4.1. 4.1 introduces the ability to buy a brothel license from the Keyholder of the Iron Bank, and then to manage your brothel holdings as a personal character interaction. You can build a variety of brothels, each employ a different class and quantity of worker. Each type of worker provides a certain return every year, increasing with quality. In addition to this, each type of brothel can be supplied with cosmetics, wigs, lingerie, bedding, medicine, aphrodisiacs, perfume, and security, each of which provide an increase in return. There is a small chance that workers can retire, or supplies can be used, the likelihood of one of these events happening increasing as you have a larger number of a greater variety. You can buy supplies for brothels without employees which will still provide some return, explainable in role play as making use of freelance workers renting rooms and buying the supplies.

Update: 4.2

Update 4.2 finishes up some message events introduced in 4.1, correct some profit margins, and expands the option to now also run a cartel in addition to a brothel, operating much the same way with the options of hashish, opium, henbane, and mushrooms.

Note: It takes time for the variables to load to start buying brothels and drug labs, when you receive your stock market traits, the variables should be loaded.

Update: 4.3

Update 4.3 corrects logged errors and brings it up to date with the game.

Update: 4.4

- Updating the mod for 1.12.*.

- Renaming it to The Imperial Treasury.

- Clearing errors from logs.