How I Lost 20kg by Tracking One Number

The Morning I Finally Got Honest With Myself

It was a Tuesday in January, and I was standing in front of my bathroom mirror holding a shirt I'd bought eighteen months earlier — a shirt that still had the tag on it because it had never fit. I put it back on the shelf. That was the moment I decided something had to actually change, not just "start on Monday" change, but real, uncomfortable, sustained change.

I'd tried things before. A juice cleanse that lasted four days. A gym membership I used twice. A keto phase that ended dramatically at a birthday party. None of it stuck because none of it made sense to me. I didn't understand why I was doing what I was doing, and the moment it got hard, I had no reason to keep going.

This time, I started with a number.

What the Number Actually Is

I'm not a nutritionist. I'm a secondary school teacher with a bad relationship with pasta. But I spent about two hours reading about something called a calorie deficit, and for the first time, weight loss clicked as a concept rather than a vague aspiration.

The basic version: your body burns a certain number of calories each day just existing — breathing, digesting, keeping your heart beating. Add in whatever movement you do, and you get your Total Daily Energy Expenditure, or TDEE. If you eat less than that number, your body digs into stored fat to make up the difference. That gap is your deficit.

I used a TDEE calculator online, plugged in my height (178cm), weight (102kg), age (34), and activity level (honestly: sedentary, despite my optimistic initial guess of "lightly active"). It spat out roughly 2,650 calories a day as my maintenance level. To lose around half a kilo per week — a rate I'd read was realistic and sustainable — I needed to eat around 2,150 calories a day. A 500-calorie daily deficit.

That was my number. 2,150.

The First Month: Boring, Revealing, Uncomfortable

I downloaded a food tracking app and started logging everything. Everything. The olive oil I cooked with. The milk in my tea. The three biscuits I had at break time without thinking about it.

That first week was genuinely upsetting. Not because the app was hard to use, but because I realised I had no idea how much I was eating. My "light lunch" was 900 calories. My "healthy" smoothie was 480. I was routinely eating 3,200 to 3,500 calories a day and wondering why I wasn't losing weight.

I didn't overhaul my diet dramatically. I just started fitting my actual food into 2,150 calories. That meant smaller portions of the things I loved, fewer mindless snacks, and learning to cook a few meals that were filling without being calorie-dense. Eggs became my best friend. So did tinned fish, which I ate with a slight sense of personal embarrassment.

By the end of month one, I'd lost 3.8kg. I know people say the first month loss is mostly water weight, and maybe some of it was. I didn't care. The scale moved in the right direction for the first time in years.

Where It Got Hard: Month Three to Month Five

I have to be honest about this part because every article I read before starting made the process sound linear. It isn't.

By month three, I'd lost about 9kg and the losses slowed down significantly. Some weeks I lost nothing. One week I gained 400 grams despite sticking to my calories, which sent me into a brief spiral of "this doesn't work and nothing matters." I ate an entire bag of tortilla chips that evening in what I can only describe as a protest vote against physics.

What I eventually understood — after some reading and a conversation with a GP — was that my TDEE had changed because I weighed less. At 93kg, my body needed fewer calories to maintain itself than it had at 102kg. The deficit I'd calculated in January was smaller now than it appeared. I recalculated my TDEE, adjusted my target downward by about 100 calories, and the slow weeks improved.

I also hit a patch in month four where I was just tired of tracking. Not physically tired — mentally tired. The constant logging felt like a part-time job. I took a week where I tracked nothing and tried to eat by feel. I gained about a kilo, mostly because my "feel" had not actually been calibrated as well as I thought. I went back to tracking. No drama, no self-punishment, just back to the number.

What Actually Helped Beyond the Calculator

The calorie deficit was the foundation, but a few other things made it more liveable:

Protein priority. Getting 130–150g of protein a day made me feel full in a way that cutting fat or carbs never did. It also made the inevitable hungry evenings much less extreme.
Cooking in bulk. Sunday afternoons became meal prep time. Having ready food meant fewer decisions when I was tired and more likely to eat something impulsive and calorie-dense.
Not labelling food as good or bad. I had pizza. I had wine at a work dinner. I had cake at my nephew's birthday. I just worked it into my weekly total rather than treating it as a failure that invalidated everything.
Walking. I started walking 8,000 to 10,000 steps a day. This wasn't a calorie-burning masterstroke — it added maybe 200 calories to my daily burn — but it changed how I felt about my body. I went from being someone who sat down whenever possible to someone who moved through the day.

The Setback I Didn't See Coming

Month seven. I hurt my knee — nothing dramatic, just my body registering that a 90-something-kilo man was now walking a lot more than he used to. I had to rest for three weeks. My activity dropped, my TDEE dropped, and I didn't adjust my eating to match. I put on 1.5kg.

Here is what I want to say about setbacks, because I think it's the most important thing: a setback is only a catastrophe if you treat it like one. I had two options. I could decide the injury proved I was doomed and quit, or I could recalculate, adjust, and keep going. The second option involved accepting that I'd lost some progress and that was just how it was.

I chose the second option. The 1.5kg came back off within three weeks of returning to normal.

The Final Months and Reaching 82kg

By month ten, I was down to around 85kg and the losses had genuinely slowed. Half a kilo every two weeks felt like all I could manage. I debated pushing the deficit harder, but I'd read enough at this point to know that very aggressive deficits often backfire — muscle loss, metabolic adaptation, the kind of hunger that makes you irrational at 9pm.

I kept my approach exactly the same and accepted the slower pace. It took until week fifty-three — just over a year — to hit 82kg. Twenty kilograms gone.

The shirt from the beginning of this story fits now. I wore it to work on a random Wednesday and nobody noticed, which felt exactly right. This was never about a moment of triumph. It was about a year of showing up for one number, adjusting it when reality required it, and getting back on track after the weeks that didn't work.

If You're Starting Out: The Practical Version

Calculate your TDEE honestly. Use a reliable calculator, input your real activity level, and don't round up.
Set a realistic deficit. 300–500 calories below maintenance is sustainable. Anything more than 750 below maintenance is usually a short-term decision with long-term consequences.
Track everything, at least for the first few weeks. You need the data. You cannot trust your instincts about portion sizes until you've calibrated them.
Recalculate every 5–8kg of loss. Your TDEE changes as you lose weight. The number that worked at the start won't work at the end.
Expect slow weeks, bad weeks, and weeks that go backwards. None of those mean you've failed. They're just weeks.

I'm not a transformation story that belongs on a magazine cover. I'm someone who found one principle that made sense, applied it imperfectly for a year, and came out the other side twenty kilos lighter and a bit less afraid of mirrors. The calorie deficit isn't magic. But it is, in my experience, honest — and honesty turned out to be exactly what I needed.