JSFiddle - React, Tailwind, and code Playground

HTML

<form action="">
  <div id='field_1' class="fields">
    <label for='donation_field'>Your Donation</label>
    <div class="dfield">
      <input id='donation_field'><br />
      <span class="subtext">Enter how much you are considering donating to PCBC</span>
    </div>
  </div>
  <br /><br />
  <div id='field_2' class="fields">
    <label for='tax_credit_field'>PA Tax Credit</label>
    <div class="dfield">
      <input id='tax_credit_field' type='text' value="" readonly=true><br />
      <span class="subtext">With a 2 year commitment</span>
    </div>
  </div>
  <br /><br />
  <div id='field_3' class="fields">
    <label for='tax_reduction_field'>Net Federal Tax Deduction</label>
    <div class="dfield">
      <input id='tax_reduction_field' type='text' value="" readonly=true><br />
      <span class="subtext">Based on 35% Tax Rate</span>
    </div>
  </div>
  <br /><br />
  <div id='field_4' class="fields">
    <label for='cost_field'>Cost To You</label>
    <div class="dfield">
      <input id='cost_field' type='text' value="" readonly=true>
    </div>
  </div>
</form>

CSS

.fields {
  width: 500px;
}

.dfield {
  display: inline;
  float: right;
}

.subtext {
  font-size: small;
  display: block;
}

input {
  float: right;
  margin-right: 150px;
}

JavaScript

document.getElementById('donation_field').addEventListener("keydown", function(e) {
  var key = e.keyCode ? e.keyCode : e.which;

  if (!([8, 9, 13, 27, 46, 110, 190].indexOf(key) !== -1 ||
      (key == 65 && (e.ctrlKey || e.metaKey)) ||
      (key >= 35 && key <= 40) ||
      (key >= 48 && key <= 57 && !(e.shiftKey || e.altKey)) ||
      (key >= 96 && key <= 105)
    )) e.preventDefault();
});

$("#donation_field").on("keyup", function() {
  var donation = $(this).val();
  var taxCredit = donation * 0.9;
  var taxReduction = donation * 0.035;
  var costToYou = donation * 0.065;

  $("#tax_credit_field").val("($" + taxCredit + ")");
  $("#tax_reduction_field").val("($" + taxReduction.toFixed(2) + ")");
  $("#cost_field").val("$" + costToYou.toFixed(2));
});