According to a survey conducted by Mic, the most common way for 18 to 34-year-olds to meet a new partner is through mutual friends. So how do you know when a friendship is turning into a romance? There are plenty of signs, but some of them are very subtle.

1. Frequency of contact

Maybe you've been friends for a while but suddenly you're messaging more often, he's liking every picture you post on social media and commenting on every status update.

Even 'accidental' contact can be telling. If you are running into each other and hanging out more often, it could be a sign that one or both of you (deliberately or subconsciously) is hanging around the places you're likely to meet, or spending more time with the friends you have in common.

2. Length of conversations

Longer and deeper conversations can just be a sign of a developing friendship...but then again, if you've always had short and superficial conversations before, but now a shared cup of coffee takes all morning, feelings could be changing.

3. Body language

Changes in body language can be so subtle they're hard to spot. Is he standing a little bit closer? Does he grab the chair next to yours in a group social setting? Touching you lightly as he tries to get past? All possible signs he's attracted to you.

4. You'll change plans for each other

We fit our lives around those who matter most. A willingness to change plans to hang out or to help each other can be a sign your friendship is deepening, but it's often a sign that it is changing into something more, too.

5. You're suddenly jealous

Jealousy isn't considered an attractive characteristic, but it can have an upside. At the very least, it can alert you to new feelings about someone who you've only ever seen as a friend. Suddenly, you're jealous of his girlfriend (if he has one) even though you used to like her. You're jealous of the girl in that picture with him on social media. You're jealous when you see a text from his ex show up on his phone.

6. He's suddenly unsupportive

If his feelings toward you are changing, he's jealous too, but you can't feel what he's feeling - you only see the resulting behavior. Jealousy will likely show up as him being suddenly unsupportive of your current boyfriend, your ex who's still interested or other guys you flirt with.

Where he might have previously said: 'You like him? I think he's single,' you'll now get: 'You like him? I heard he's a jerk.'

7. You're both (finally) single

Often, the thing that stops a relationship developing between two friends is the simple fact that you're both dating other people.

If you're both finally single at the same time, that may not be a coincidence. If he ends a relationship as soon as he finds out you're single, or you suddenly 'realize' your current man isn't the one for you the moment your friend breaks up with his girlfriend, that could mean it's time to date each other.

8. Nervousness or awkwardness

We're relaxed with our friends. We're nervous around people we're attracted to. Sudden awkwardness could just be a sign you've both admitted to yourselves you have feelings for each other.

9. The flirting starts

You don't always notice when friendliness becomes flirtiness. Watch (and listen) closely to see if he's flirting or just being friendly. As things progress it will become more obvious. You're touching him. He's paying you compliments. There's way too much eye contact. The flirting has begun in earnest.

10. You want to share things with him first

If you want to share good news with him before anyone else, or cry on his shoulder when it all goes wrong, there's probably more than friendship going on.

11. You try and mention him more often

When he's not around you find that all your stories feature him, and you hear yourself repeating things he's said to you.

12. Your other friends start to notice

Your mutual friends make comments on how much time you're spending together. You start to get the question: 'Is something going on between you guys?' And even though you initially say 'no', you still ask your mutual friends if they've noticed the changes, too.

13. What you call each other changes

Some people call everyone 'honey' or 'sweetie'. But if you've suddenly developed pet names for each other, that probably means something.

14. He tries to get you alone

He'll offer you a ride home or 'accidentally' run into you in a coffee shop, just to get some one-on-one time with you.

15. He asks you out

This is the most obvious sign your friendship is moving into new territory. But sometimes it can still be ambiguous, so be prepared to clarify. If he suggests dinner it's OK to ask outright: 'Are you asking me on a date?' No-one wants to be on what they think is a date only to realize he still thinks of you as a buddy.

When it comes down to it, the only clear sign that your feelings of friendship have turned into deeper feelings is when you tell each other. If all the other signs are there, it's probably time to take that risk.