dEURO

# Savings & Interest

Earn interest on your Decentralized Euros through the built-in savings module.

The dEURO system includes a native savings feature that allows dEURO holders to earn interest simply by depositing their tokens. The interest rate is governed by nDEPS holders through the Leadrate mechanism, and the same Leadrate also drives the interest charged on borrowing positions — so saving and borrowing rates always move together.

# How Savings Work

When you deposit dEURO into the savings module, your tokens start earning interest immediately. The interest accrues continuously based on the current Leadrate.

Feature Description
No lock-up period Withdraw anytime
Continuous interest Interest accrues every second
Compound on refresh Claim interest to start earning interest on interest
Governance-controlled rate nDEPS holders vote on the interest rate
Fully segregated Your saved dEURO stays attributable to you and is not used to back loans

The 3-day lock-up before deposits could be withdrawn, present in Frankencoin's savings design, was removed in dEURO without replacement. Deposits can be withdrawn at any time.

# The Leadrate System

The Leadrate (from German Leitzins, "base rate") is the system-wide interest rate that affects both savings yields and borrowing costs.

# How Rates Are Set

  1. A qualified nDEPS holder (with ≥2% voting power) proposes a new rate.
  2. The proposal enters a 7-day timelock.
  3. After 7 days, anyone can execute the change.
  4. The new rate takes effect immediately.
Current Rate → Proposal → 7-Day Wait → New Rate Active

# Rate Mechanics

The Leadrate uses a "ticks" system for precise interest calculation:

  • 1 tick = 1 PPM-second (parts per million per second).
  • Interest accumulates as ticks over time.
  • When you refresh your balance, ticks are converted to dEURO.

Example: at a 5% annual rate (50,000 PPM):

  • 1 day = 50,000 × 86,400 = 4,320,000,000 ticks.
  • On 10,000 dEURO that is roughly 1.37 dEURO interest per day.

# Initial Rates at Deployment

Module Initial Leadrate at deploy
V2 (SavingsGateway) 10% (100,000 PPM)
V3 (Savings) 8% (80,000 PPM)

The current rate is whatever nDEPS holders have voted in since launch — check currentRatePPM() on the active savings contract.

# Using the Savings Module

# Depositing dEURO

  1. Open the Savings page (opens new window) in the app.
  2. Enter the amount of dEURO you want to deposit.
  3. Approve and confirm the transaction.
  4. Your dEURO immediately starts earning interest.
function save(uint192 amount) external
function save(address owner, uint192 amount) external

// V2 SavingsGateway variants with frontend code:
function save(uint192 amount, bytes32 frontendCode) external
function save(address owner, uint192 amount, bytes32 frontendCode) external

# Checking Your Balance

Your savings balance consists of:

  • Principal: the dEURO you have deposited.
  • Accrued interest: interest earned since the last refresh.
function savings(address account) external view returns (uint192 saved, uint64 ticks)
function accruedInterest(address accountOwner) external view returns (uint192)
function accruedInterest(address accountOwner, uint256 timestamp) external view returns (uint192)

# Withdrawing dEURO

You can withdraw your dEURO plus earned interest at any time:

function withdraw(address target, uint192 amount) external returns (uint256)
function withdraw(address target, uint192 amount, bytes32 frontendCode) external returns (uint256)

# Refreshing Your Balance

To compound your interest (earn interest on interest):

function refreshMyBalance() external returns (uint192)
function refreshBalance(address owner) external returns (uint192)

Refresh periodically to maximise compound interest. For very small balances, the gas cost can outweigh the compounding benefit.

# Interest Source

Interest paid to savers comes from the system's equity pool via dEURO.distributeProfits(). As a consequence:

  • Interest is only paid as long as there is sufficient equity.
  • The current equity() value caps available funds.
  • If equity is depleted, interest payments are capped or paused.

This creates a natural balance: high savings rates attract deposits but reduce equity, while low rates preserve equity but may cause withdrawals.

# SavingsVault (svDEURO, ERC-4626)

For DeFi integration, dEURO provides an ERC-4626 compatible vault wrapping the savings module. ERC-4626 is the "tokenized vault standard" — a standard interface for yield-bearing tokens that makes the vault easy to plug into other DeFi protocols.

# Vault Mechanics

Concept Description
Shares (svDEURO) Represent your proportional ownership of the vault
Assets (dEURO) The underlying tokens in the vault
Price per Share Increases over time as interest accrues

Example:

  1. You deposit 1,000 dEURO when price = 1.00 → receive 1,000 svDEURO.
  2. Interest accrues, price rises to 1.05.
  3. Your 1,000 svDEURO is now worth 1,050 dEURO.

# Vault Functions

function deposit(uint256 assets, address receiver) external returns (uint256 shares)
function mint(uint256 shares, address receiver) external returns (uint256 assets)
function withdraw(uint256 assets, address receiver, address owner) external returns (uint256 shares)
function redeem(uint256 shares, address receiver, address owner) external returns (uint256 assets)
function price() external view returns (uint256)
function totalAssets() external view returns (uint256)

# Inflation Attack Protection

The vault uses OpenZeppelin's virtual-shares pattern to prevent "inflation attacks" where a malicious first depositor could manipulate the share price. A small virtual offset is added to share-price calculations.

# V2 vs V3 — Which to Use?

Both savings modules are permanently deployed and accept new deposits. They share the same dEURO token and equity pool, but differ in plumbing:

V2 (SavingsGateway) V3 (Savings)
Frontend rewards Yes — 5% of earned interest goes to the frontend code, see Frontend Rewards No — V3 bypasses the FrontendGateway entirely
Optional savings interest compounding Yes Yes
Vault address 0x1e9f008B1C538bE32F190516735bF1C634B4FA40 (opens new window) 0x75Beb37A3C86eE4c38931E2a9319E078da612979 (opens new window)
Savings address 0x073493d73258C4BEb6542e8dd3e1b2891C972303 (opens new window) 0x760233b90e45d186A9A98E911B115F7F4B90d3D9 (opens new window)

If you are a frontend operator and want to earn referral rewards on your users' savings interest, route them through the V2 SavingsGateway. Otherwise the V3 module is the default for new integrations.

# Interest Calculation Example

Scenario: 10,000 dEURO deposited at a 4% annual Leadrate (40,000 PPM) for 30 days.

Daily interest      = 10,000 × (40,000 / 1,000,000) / 365 = 1.096 dEURO
30-day interest     = 1.096 × 30 = 32.88 dEURO
With daily compound ≈ 32.96 dEURO (slightly more)

# Savings vs. nDEPS

Aspect Savings (dEURO) Pool Shares (nDEPS)
Risk Low — principal preserved while equity is intact Higher — value moves with system results
Return Leadrate Fees and liquidation profits, variable
Governance None Voting power that grows with holding time
Lock-up None 90 days before redemption is allowed
Best for Stable yield seekers Active participants in the system

# Important Notes

  1. Module disabled when rate is zero — savings module deposits revert with ModuleDisabled once the Leadrate is 0%. The contract also pre-empts a queued 0% rate change: as soon as the 7-day timelock to a proposed 0% rate has elapsed (so applyChange() is callable), new deposits are already blocked.
  2. Interest cap — interest payments are capped by available equity. In extreme scenarios, you may receive less than expected.
  3. No deposit insurance — unlike traditional bank deposits, there is no insurance. The safety of your funds depends on the overall health of the dEURO system.
  4. Gas costs — consider gas costs when deciding how often to compound. For small balances, frequent refreshing may not be economical.

# Events

event Saved(address indexed account, uint192 amount);
event InterestCollected(address indexed account, uint256 interest);
event Withdrawn(address indexed account, uint192 amount);
event RateProposed(address who, uint24 nextRate, uint40 nextChange);
event RateChanged(uint24 newRate);

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