You do not need to "rate" the breakers - what you have is fine.

Load diversity means you are very unlikely to have all the loads on, and pulling their maximum current at the same time.
When you do a load calculation you use either the heating or cooling, whichever is larger, since they are not used at the same time in most residential equipment (there are commercial settings that use both for humidity control).

The sum of the breakers says nothing about what is being used.

Double pole breakers are not 'cut in half.'
They supply up to their rated current from both legs at the same time (for a 240 V load) or either leg separately (for 120 V loads).

If you have 100 A mains, they will trip if you overload the leg they are on.

The rating of the panel as 125 A is based on the size of the buses, and is a 'peak' allowed current.

What do you want to plug into the outlets you're adding?

If you're anything like 90% of the people I end up doing work for, whatever it is, you're already using it - but you've been plugging it into extension cords and running them through your kitchen window for the last two and a half eons. If this is the case, then you've already done your "load calculation" via the try-and-see route. You plugged the stuff in, you didn't trip your main breaker. Therefore, you have enough available current to use those devices, so go ahead and add your outlets.

I wholly reject load calculations for adding circuits and devices. They're a good thing for new installations, but for adding an outlet or two? C'mon.

When you go over the limit, your main breaker trips. Guess what? That's highly annoying. So you take the hint, and upgrade your service. I've never had it happen anyway.

It is as better method than guessing and waiting for the main to trip.

Measuring the loads is also adequate.

"When you go over the limit, your main breaker trips. Guess what? That's highly annoying. So you take the hint, and upgrade your service. I've never had it happen anyway."

I have upgraded services based on adding new large loads to the house.
A couple times for adding central air to 1950s houses, and a couple times to get enough power to run my shop equipment.

Customers are going to be really mad if you add new loads (even at their request) and then have to come back and upgrade the service.

It is not a good way to keep customers and get recommendations.

If you want to play games in your own house, have at it.

Large loads, sure. A couple outlets? Gimme a break.

Customers are going to be really mad if you add new loads (even at their request) and then have to come back and upgrade the service.

It is not a good way to keep customers and get recommendations.

There are two ends of the DIY---business scale. There's also a great deal in between.

I would argue that my earlier statements are 100% true on the DIY end, and would also 100% agree with you on the business end. ie, my statements were not ever intended to apply to an electrician doing such work as a business. When doing something for paying customers, certainty is very important.

I am somewhere in the middle of the scale. I am not in business as an electrician. I do, however, do a lot of work for friends, most of whom fully understand what I'm doing and just don't want to be bothered to do it themselves. One is actually a licensed electrician who is employed at a paper mill, and simply doesn't have time to do much work at home. If you're working on your own project, "try and see" is a perfectly valid method - and that is, in fact, what the original poster is doing.

Measuring the loads is also adequate.

I wouldn't even come close to arguing with that.

As I said, I've never actually tripped a main, and I guess I should alter things a little bit by stating that I apply a lot of subjective, "wow, this house must use a lot of power", mental "measurement".

Put differently. If your customer's main trips, they're going to pissed. In my case, however, before I even did the work, I already told the "customer", who is a known friend, "uhh, you're probably pretty close to the limit so it wouldn't surprise me if we have to do this, this, that, and the other thing soon." I have advised the person of the possibilities and what they mean. "Customer" then decides whether or not I continue, and is not surprised with either outcome.

Bad terminology.

An "outlet" is any place utilization equipment is connected.
My arc welder uses an outlet, and is a 50 amp, 240 V load.

A few receptacles are not likely, but a 20 amp mutiwire to a garage could be a decent load depending on what is plugged into the receptacle.

No, I had to make a guess about what you meant.

Guessing is NOT a good option in electric wiring.

It tends to cause problems if not immediately, then further down the road.

The original poster is talking about adding some receptacles. For me to utter the phrase in question, in reference to anything OTHER than receptacles, would show a failure to follow conversation on my part.

I am not one of this forum's frequent spouters of misinformation. I don't know why the hell you've chosen to go after me on this one, but I'm not leaving this forum, nor shall my view on this subject waver.

I will not be following this thread any further.

My original statement stands. I do NOT believe any effort in "load calculation" is necessary for the original poster to add some freakin outlets, or receptacles, for that matter.