How make addition variable date with integer on twig?

Question

I have this code:

{% set varfechainiciocontratoprincipal = entity.proyectos.fechainiciocontratoprincipal|date('Y-m-d') %}

the content is varfechainiciocontratoprincipal: 2015-01-10

And other variable:

{% set varduracioncontratoprincipal = entity.proyectos.duracioncontratoprincipal %}

the content is: 540

How make this:

varfechainiciocontratoprincipal + varduracioncontratoprincipal|date("Y-m-d")

I need of result in this format: 2016-10-10 (Is a example)

---

I probe this format:

{{ varfechainiciocontratoprincipal|date_modify("+540 day")|date("m/d/Y") }}

This work but I need that of number 540 is a variable.

Answer 1

This is actually a time where Twig acts more like PHP where I would use string concatenation to solve the problem.

For ease of reading (and future visitors) I create my own variables:

{% set modify = '540' %}
{% set date = "now"|date("m/d/Y") %}

{{ date|date_modify("+" ~ modify ~ " day")|date("m/d/Y") }}

Result (as of today): 08/31/2016