Demonstrates using date-fns to compare days differences

App.js

import differenceInDays from 'date-fns/difference_in_days'

// Last day of tax year: 5th April 2018
const lastDayOfTaxYear = new Date(2018, 4, 5, 0, 0);

// My birthday: 18th September 2018
const myBirthday = new Date(2018, 9, 18, 0, 0);

const daysDiff = differenceInDays(myBirthday, lastDayOfTaxYear);

const content = document.createElement('p');
content.innerHTML = `<p>There are ${daysDiff} days between 
the last day of tax year and my birthday</p>`;

document.body.appendChild(content);