Не знаю почему не работает
 

:help:

<input autocomplete="off" class="form-control amount input-lg" id="inputAmountCrypto" onchange="updateCurrencyLTC(value)" name="crypt_amount" placeholder="0.00144467" type="text" value="">

<?php
echo "<script>";
echo "function updateCurrencyLTC(value) {";
echo "document.getElementById(\"inputAmountUsd\").innerHTML = value * $ltc;";
echo "}";
 echo "</script>"
?>

У меня работает...

<input autocomplete="off" class="form-control amount input-lg" id="inputAmountCrypto" onchange="updateCurrencyLTC(value)" name="crypt_amount" placeholder="0.00144467" type="text" value="">
<div id='inputAmountUsd'></div>
<script type='text/javascript'>
function updateCurrencyLTC(value) {
	document.getElementById("inputAmountUsd").innerHTML = value;
};
</script>

Забыл дать, это редактирую, но не хочет

<input class="form-control amount input-lg"  id="inputAmountUsd" value="" name="usd_amount" placeholder="" type="text" autocomplete="off">

:-?

В JS не шарю... innerText использовать?

petrdobroskok1975,

function updateCurrencyLTC(value) {
	document.getElementById("inputAmountUsd").value = value;
};

petrdobroskok1975,

<?php
echo "<script>
function updateCurrencyLTC(value) {
    var c = $ltc;
    document.getElementById(\"inputAmountUsd\").value = value * c;
}
</script>"
?>