How to know when to increase your weights

Have you ever finished a set and wondered if you are lifting heavy enough?

One of the hardest parts of training without a coach to guide you for every session, is figuring out the right weights to lift.

When I first started training, I stayed at the same weight for months. The workout felt hard, so I figured I was doing enough. It wasn’t until I started actually lifting heavier, slowly increasing my weights, that I realised I was actually a lot stronger than I thought.

If you’ve ever stood at the rack wondering when to go heavier then this post is for you.

The most common mistakes people make when selecting their weights

Too cautious. You keep the same weight for week after week because it still feels like “enough” — it’s challenging, you’re tired after, so it must be working. I’ve made this exact mistake. I followed a plan that repeated the same numbers for 2 months and mistook the consistency for progress.

Too aggressive. You keep adding weight because it feels good to push yourself, without making sure your body is ready to handle that weight just yet. I’ve made this mistake too and can confirm this is the version that leads to a shoulder that’s annoyed with you for months.

Both mistakes come from the same root problem: judging a set by how it felt in the moment, instead of by what actually happened during it, and the training you’ve done up until then.

The easiest way to know - reps in reserve

Instead of asking yourself “did that feel hard” ask “how many more reps could I have done.” That’s reps in reserve (RIR), and it’s the basis of the RPE scale validated specifically for resistance training, which ties perceived effort directly to how many reps you had left in the tank rather than a vague sense of difficulty.

RIR is still an estimate, not an exact count — you’re guessing how close you were to failure, not measuring it. Research on predicting reps to failure found people reliably underestimate how many reps they actually have left, and the gap is bigger the newer you are to training — the least experienced lifters in that study underpredicted by 4–5 reps, the most experienced by 1–2. So trust the number, but hold it a little loosely, especially early on.

Here’s a simple, practical way to use it:

• 2+ reps left at the top of your target range → you’re probably ready to add weight next session.
• 0–1 reps left, but your form held up clean the whole set → stay at this weight one more session before moving up.
• You needed to grind, break form, or bail on a rep to hit the target → don’t add weight yet. If anything, this is a session to consolidate.

That’s it. Get in the habit of counting how many good reps you leave on the table, not just how a set felt.

Three checks before you actually add the weight

Reps in reserve tells you whether you’re ready. These three catch the cases where the number looks right but something else says wait.

1. Was your form clean? There’s a difference between “I did five clean reps” and “I did five reps and the last two were more momentum than muscle.” If your range of motion shrank, your tempo sped up, or a joint took over for a muscle in the last couple of reps, that set doesn’t count as a clear pass — even if the number of reps matches the plan. Better execution is one of the four legitimate ways to progress — progression isn’t only about adding load. Doing the same weight with better control, technique, or range of motion is a real improvement in its own right. Bank that before you add more weight on top of it.

2. Did this happen once, or has it happened for two sessions in a row? One easy-feeling set can be a fluke — you slept well, fueled well, or just had a good day. A systematic review of autoregulation methods found that using real-time signals like RPE to adjust load is an effective way to build maximal strength — but in my own training, I’ve learned to trust it more once it repeats than the first time I see it. If this is the second session in a row where the same weight left 2+ reps in reserve, that’s a real signal. If it’s the first time, it’s worth noting, not necessarily acting on yet. This “twice in a row” detail isn’t arbitrary — it’s the same trigger point behind double progression, the standard framework for deciding whether to chase another rep or add weight next.

3. How’s everything outside the gym been? A weight that suddenly feels easy after a rough week of sleep isn’t always progress — sometimes it’s a lighter perceived load because your nervous system had an off day at reading effort accurately, and sometimes it swings the other way, where genuine progress gets masked by fatigue and reads as “still hard.” If sleep, stress, or soreness have been noticeably off, treat this session’s RIR reading as less reliable than usual, not as the final word.

What adding weight should look like

Once you’ve cleared those checks, keep the jump small. The instinct is to add a satisfying amount — the number that feels like it proves something. Resist it.

The ACSM position stand on resistance training progression backs this up: once you can comfortably beat your target rep range by 1–2 reps, it recommends a roughly 2–10% load increase — not a dramatic jump that outruns what your body’s actually adapted to. In practice, that’s the smallest increment your equipment allows, leaning toward the lower end of that range for smaller or more technical lifts — enough to matter over months, small enough that a single jump never turns into the reason your next three sessions are wrecked.

When the honest answer is hold, not add

Sometimes every check above says wait, and that’s not a failure. It just means you need a little more time. A controlled study on a planned one-week deload compared lifters who took a scheduled recovery week against a group that trained straight through for the same nine weeks — the deload group ended up with essentially the same muscle size, though their strength gains came in a bit behind the group that never stopped. A week off didn’t erase their progress; it cost a little on the margin, not the whole account. Holding at your current weight, or backing off for a week, isn’t the opposite of progress — it’s not going to outperform pushing through, but it’s not going to wipe out what you’ve already built either.

TLDR;

Stop asking if a set felt hard, and start counting how many more reps you think you could do. And test it. Sometimes you are stronger than you realise.

If you finished with two or more clean reps left in the tank, and it’s not the first time, add a small amount of weight. If you had to fight for the last rep, or it’s the first easy session after a run of hard ones, give it one more week before you decide.

Sources

• Zourdos MC, Klemp A, Dolan C, et al. Novel Resistance Training–Specific Rating of Perceived Exertion Scale Measuring Repetitions in Reserve. Journal of Strength and Conditioning Research, 2016.
• Steele J, Endres A, Fisher J, Gentil P, Giessing J. Ability to predict repetitions to momentary failure is not perfectly accurate, though improves with resistance training experience. PeerJ, 2017.
• Effects of subjective and objective autoregulation methods for intensity and volume on enhancing maximal strength during resistance-training interventions: a systematic review. PeerJ.
• American College of Sports Medicine. Progression models in resistance training for healthy adults. Medicine & Science in Sports & Exercise, 2009.
• Gaining more from doing less? The effects of a one-week deload period during supervised resistance training on muscular adaptations. PeerJ.