This calculator is an estimation of the rewards that you get from staking ROME on RomeDAO. The estimations for the decrease in APY in RIP-003, are calculated as follows:

const SUPPLY_LIMITS = {  REGAL: {
    MAX: 1000,
    MIN: 10,
    DURATION: 6 * 31,
    MAX_SUPPLY: 10000000,
    MIN_SUPPLY: 500000,
  },
  REPUBLICAN: {
    MAX: 10,
    MIN: 1,
    DURATION: 24 * 31,
    MIN_SUPPLY: 10000001,
    MAX_SUPPLY: 1000000000,
  },
  IMPERIAL: {
    MAX: 1,
    MIN: 0.03,
    DURATION: 7 * 31,
    MAX_SUPPLY: 100000000000,
    MIN_SUPPLY: 1000000001,
  },}
calculatedAPY = SUPPLY_LIMITS.REGAL.MAX -
            (estimatedTotalStakedSupply / SUPPLY_LIMITS.REGAL.MAX_SUPPLY) *
            (SUPPLY_LIMITS.REGAL.MAX - SUPPLY_LIMITS.REGAL.MIN)

So in short the APY is equal to APY Era Max - [(staked total/staked supply MAX for that era) * difference between ERA APY MAX and MIN]

Note: that all of this is just an estimation, so your actual rewards can vary.

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