There are various reasons why a couple decides not to spend money on contraception, but these do not matter as long as they use some ways of protection against unwanted pregnancies. These methods include pulling out, the calendar method and taking temperatures every morning.
When you are opting for interrupted intercourse, then you need to consider that even pre-ejaculate can contain sperms and even they are enough to fertilize an egg, and this is why it is not safe. However, if the penis is pulled out of the vagina before ejaculation, then it is still better than letting the semen squirt inside. Obviously, anal or oral sex is also a possible solution, since it prevents sperms to enter the vagina and the uterus.
If you want to make sure that even if it gets inside the woman's body, it is not going to end with pregnancy, then you should also consider using the calendar method. For this, you need to know the first day of the menstruation cycle – when the period starts – and add 14-20 days to it. Those are the most fertile days. The least fertile ones are the days before the bleeding starts. If you do not want to count the days, then you can also use thermometer. If a girl takes her vaginal temperature every morning. When it raises, that day will be more fertile than the others.
However, if you do not want to use medical or surgical contraception then you should mix all of these natural methods.