Calculate investment's compound growth

compound-growth.js

// Calculates the compound growth of an investment over number of periods.
// Assumes fixed regular contributions and average growth rate.
function compoundGrowth(startingBalance = 0, periodContribution = 100, periodGrowthRate=0, nPeriods = 1, currencyLabel = '£') {
    const totalContribution = startingBalance + periodContribution * nPeriods;
    const finalBalance = [...Array(nPeriods)].reduce((runningBalance) => {
        return runningBalance + (runningBalance * periodGrowthRate) + periodContribution;
    }, startingBalance);
    const absoluteGrowth = finalBalance - totalContribution;
    const relativeGrowth = absoluteGrowth / totalContribution;
    console.log(`${currencyLabel}${finalBalance.toFixed(2)} will be returned after ${nPeriods} periods with ${currencyLabel}${periodContribution.toFixed(2)} contributed each period and an average period growth rate of ${periodGrowthRate * 100}% and initial lump sum of ${currencyLabel}${startingBalance}.
        Absolute Growth: ${currencyLabel}${absoluteGrowth.toFixed(2)}
        Relative Growth: ${(relativeGrowth * 100).toFixed(2)}%`);
    return finalBalance;
}

compoundGrowth(0, 100, 0.005, 12);