The guide

How heavy to start, and when to add weight

Start light, stop each set with a few reps to spare, and add a little weight once you reach the top of your range.

4 min read · Updated 20 October 2026

A common first question at the gym is how much to lift. The honest answer is that nobody knows your number yet, not even you. You find it by trying, and it's fine to start light. Here is how to pick a first weight, and how to tell when it's time for more.

Three words first

A rep (short for repetition) is one complete lift of the weight, start to finish.
A set is a group of reps done one after another without stopping, such as 10 in a row.
Rest is the break between sets.

Reps left in the tank

"Reps left in the tank" means how many more reps you could have done when you stopped. Trainers call it reps in reserve, or RIR. If you finish 10 reps and could have done 2 more cleanly (smoothly and under control, without jerking or twisting), you had 2 left.

Health guidelines put the effort simply. The US physical activity guidelines say to keep going until one more rep would be hard. The UK's National Health Service (NHS) says to work until you need a short rest before you could go again.

You don't need to go to failure, the point where you can't finish another rep. In a review published in 2026, the American College of Sports Medicine (ACSM) found no extra benefit from going to failure. It suggests stopping near failure, about 2 or 3 reps short, as enough effort, though it says the exact number isn't settled.

How many reps to aim for

A rep range is the number of reps you aim for in each set, such as 8 to 12. For beginners, 8 to 12 is a good place to start. The US guidelines say one set of 8 to 12 reps per exercise works, and 2 or 3 sets may work better.

Finding your starting weight

Choose a weight you think you could lift 8 to 12 times with 2 or 3 left. If you have no idea, choose one that feels clearly light.
Do reps until you think you have 2 or 3 left, then stop and count.
If you did more than 12, go a little heavier on your next set. If you did 8 to 12, keep that weight: you've found it. If you stopped before 8, go lighter.

Expect your first guesses to be off. That's normal. A review of studies found that people tend to guess about one rep too few, beginners and experienced lifters alike: they had a little more left than they thought.

When to add weight, and how much

Progressive overload is the trainers' name for asking a little more of your muscles over time: more weight, reps, sets or days a week. The US guidelines say strength builds this way, a little at a time.

Your target is the top of your range: 12, if you aim for 8 to 12. When you reach it with 2 or 3 reps still left, add 2 to 10 percent next time. At 100 pounds that's 2 to 10 pounds; at 50 kg, 1 to 5 kg. If your gym's weights don't go up that little, use the smallest step they have.

This follows ACSM's 2009 advice to add 2 to 10 percent once you can do 1 or 2 reps more than your target. Reaching 12 with 2 or 3 left means you could have done 14 or 15.

At the new weight, stay until you reach your target with 2 or 3 left again, then add again.

Why starting light is fine

The US guidelines' advice for people who haven't been active is to "start low and go slow".
ACSM's 2026 review found muscle grew about the same with light and heavy weights (down to about a third of the most you could lift once). It adds that the effort has to be enough, such as stopping about 2 or 3 reps short of failure. Heavier weights did best for strength.
Starting light is a beginning, not the whole plan. The same review found the first benefits come even before you add weight, but to keep making progress you need to ask a little more over time: more weight, reps or sets.

Stay safe

Check with a doctor before you start if you have a health condition, are pregnant, or haven't exercised in a long time.
Stop right away if anything hurts, or if you feel dizzy or have chest discomfort. If a new symptom comes up, talk to a doctor.

In the app

When you choose a plan, Train Personal says it plainly: "Start light. The first 2 workouts find your weights." It asks "How hard was that?", and you can answer with one of five effort words. When it's time to add weight, it tells you and says why. Nothing changes unless you tap it.