BTC till 2017

var price = 910, // current price
    percentage = 5, // current percentage
    accumulator = 0.1; // or 0.0, or -0.1

[...Array(8).keys()].forEach(e => { // days till 2017
    price += (price / 100) * (++percentage + percentage * accumulator);
    console.log(`day:${31 - 7 + e} %:${percentage} price:${price}`);
});