consider these fields in a QWeb template:

<t t-set="tiempo" t-value="r.saida-(r.saldo/100)"/>
</t>
    <tr>
        <td colspan="7" class="align-center" align="center">
            <b>Tienes <span t-esc="tiempo"/> dias de cash</b>
        </td>
    </tr>

Here, tiempo is just a field I've set up on QWeb view, which makes a little arithmetic operation.

Doesn't exist on model, but saida and saldo do exist, so, is there a possibility to add this tiempo to an email template?

I mean without creating this very same operation on model?