I’m gaining weight now that I’m exercising

It is very common to see an increase in weight when you start a new exercise regime (or make drastic changes to an existing one). It's water retention. As long as you are sure you are not eating more, and there are no hormonal fluctuations to take into account, then it should settle back to where you expect it to be within the next couple of weeks. Hang in there.

It takes weeks to build muscle. You are probably inflamed as a beginner and are retaining water for the repair. Exercise also brings metabolic changes and your body will store glycogen for you to use, and to store it, it needs water.

Do not eat the "lost gym calories" , focus on keeping the calories going in regardless of activity level. Focus on anti-inflammatory foods, so increase vegetables and decrease meats/fat.

How long are your sessions?

due on in the next week or so?
pregnant?

or do you need to lower your calorie intake?
are you definitely tracking everything, correct portion sizes, every little snack, or calorie filled drink. even at the weekend. and leaving yourself in a deficit of approx 3500 calories per week?

are you over estimating how many calories you’re burning in exercise?

there’s just no way you’re moving more, eating the same and gaining weight - as in fat rather than water retention.
and there’s absolutely no way you’re gaining that much muscle that quickly unless you have some sort of medical issue.

well done for being more active though op. Fingers crossed it comes back off for you

Hormones?

It is very, very common for people to start eating more when they start exercising more, and they don't even realise it.

I don’t think you would gain muscle from what you are doing (cardio), if you were doing weights then I would expect a gain.

I exercise a lot and find that it just makes me really hungry so I don’t necessarily lose weight from exercising but it benefits me in other ways and helps tone.

God seriously, get off the scales. Do you feel healthier? Are you less out of breath? Are you sleeping better? Weight is pretty unimportant, good health is what counts.

your muscles start to hold an extra few lbs of water weight when you're new to working out. if it's under 5lbs it will be that.

That is because muscles weigh heavier than fat

That phrase is just a shorthand way of saying it is more dense than fat, as PPs explained. A lb of a thing is still a lb!

However when the phrase 'muscle weighs more than fat' is used, it's taken that it refers to density.

I think it's more likely that the exercise is making you hungrier and you're eating more than you're burning off. Could that be correct OP?

Really funny that muscle doesn’t weigh more than fat - a god damn gym instructor told me that just the other day. 😂 😂 Didn’t mean to mislead Op, just trying to be supportive and what I was taught at a gym. Hope you keep up the good work!!

There’s no way you have gained several pounds of muscle in a fortnight.
you may be gaining muscle if you’ve literally never done any exercise before, but not that much.
I’d guess that you’re hungrier and getting a bit slack with calorie counting / monitoring what you eat. Or you could be due on. Or you may be drinking more water.
the gym is a red herring - correlation isn’t causation

Tired muscles cause water retention as they recover. This is a good process for strengthening muscle long term and the water weight is not harmful. You'll look leaner for it despite what the scales say.

darnit, teach me never to use dashes and to preview (!!)

This blog talks about women typically able to gain about 0.5 lbs/muscle per month over a 4.5 month period, when they start weight-lifting which is obviously activity focused on muscle gain not cardio benefits. The per month gain in muscle slows down after the first 1-2 months. Because there are physical limits to how much muscle a person can gain, how much body composition altering is possible. MNers talking about 2 kg gains in muscle over short periods make me laugh. Fat people often already have a lot of muscle from hauling all those extra kg around with them everywhere.

You’re likely building muscle OP

Nobody puts on several pounds of muscle in 2 weeks doing walking and crosstrainer. Water retention and increased appetite.

Sorry, I was one of the ones who said that and you're totally right. I was being very lazy at explaining what I meant and used a shorthand which was very unhelpful.

You’re likely building muscle OP and muscle weighs more than fat

A pound of muscle weighs the same as a pound of fat. They both weigh a pound.

While it's true that muscle weighs more than fat no it's not, a lb of anything weighs a lb!!
Muscle is more dense than fat so a lb of muscle (as illustrated above) takes us less space than a lb of fat. That said, as women it is very hard to build any serious amount of muscle unless you lift very heavy weights several times a week, eat a protein rich diet, and probably take supplements. The OP hasn't even mentioned lifting a weight so it's unlikely to be that in a short space of time!

It is categorically NOT true that muscle weighs more than fat - no idea why that keeps being trotted put as it's a myth as a quick google will reveal.

It is however denser and takes up less space

That is to say, I am eating actually the same amount of calories to lose weight as I did 20 years ago, but I was much lighter 20 years ago to start with.