# Payments & EMI

Trilobyte uses an **Equated Monthly Instalment (EMI)** model for loan repayments. Each payment is a fixed amount calculated at disbursement, covering both principal and interest.

## EMI Calculation

The EMI is calculated using the standard amortisation formula:

$$
EMI = P \times \frac{r(1+r)^n}{(1+r)^n - 1}
$$

Where:

* $P$ = Principal (loan amount)
* $r$ = Monthly interest rate (annual rate ÷ 12)
* $n$ = Number of monthly payments (loan term)

{% hint style="info" %}
All math is **integer-only** — Soroban has no floating-point support. Trilobyte uses 10¹² internal precision scaling and ceiling-rounds the final EMI to ensure the borrower always repays at least the full amount owed.
{% endhint %}

## Payment Split

Each payment is split into two pools based on the vault's **split ratio**:

| Pool          | Purpose                                                 | Accessible By                |
| ------------- | ------------------------------------------------------- | ---------------------------- |
| **EMI Pool**  | Investor yield — proportional to split ratio (e.g. 80%) | Investors via `claim_yield`  |
| **Cash Pool** | Borrower operating capital — remainder (e.g. 20%)       | Borrower via `withdraw_cash` |

For example, with a split ratio of 80 and a payment of 10,000 USDC (after fees):

* **8,000 USDC** → EMI pool (investor yield)
* **2,000 USDC** → Cash pool (borrower operating capital)

## Payment Schedule

* Payments are due every **30 days** (30/360 day-count convention)
* The first payment is due 30 days after disbursement
* Each payment advances the `next_due` date by 30 days
* The total number of payments equals the loan term in months

## Principal Amortisation

Each EMI payment contains both an interest component and a principal component:

$$
\text{interest} = \text{outstanding} \times \frac{\text{annual\_rate}}{12}
$$

$$
\text{principal} = \text{EMI} - \text{interest}
$$

The outstanding principal decreases with each payment. Early payments are interest-heavy, while later payments are principal-heavy — standard amortisation behaviour.

## Protocol Fee

A **0.5% protocol fee** is deducted from every payment before the split:

1. Payment received (e.g. 10,000 USDC)
2. Protocol fee deducted (50 USDC → treasury)
3. Remainder split by ratio (9,950 USDC → EMI + Cash pools)

## Yield Claiming

Investors claim their share of the EMI pool proportionally:

$$
\text{claimable} = \frac{\text{balance}}{\text{total\_supply}} \times \text{emi\_pool} - \text{already\_claimed}
$$

* `balance` = Investor's debt token balance
* `total_supply` = Total debt token supply
* `emi_pool` = Total accumulated EMI pool
* `already_claimed` = Amount the investor has already claimed

Claims can be made at any time during the **Active** or **FullyRepaid** phases.

## Token Precision

All amounts use **7 decimal places** (Stellar standard). For example:

* 1 USDC = `10_000_000` (10⁷)
* 0.5% fee = `50_000` in 7-decimal format


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