How your FICO score is actually built

Most people meet their credit score as a single number that appears, moves, and disappears without explanation. It feels like weather. It isn’t. A FICO score is a calculation, and a calculation has inputs. Once you can name them, the number stops being something that happens to you and becomes something you can read.

Here is the whole machine, in plain language.

The five inputs

FICO weighs five categories. The percentages below are the classic, published weights for the general-purpose models — your exact mix shifts with your file, but this is the map.

• Payment history — about 35%. Did you pay on time? This is the single largest lever. One 30-day late payment does more damage than most people expect, and it lingers.
• Amounts owed — about 30%. Mostly this is your utilization: how much of your available revolving credit you’re using. Lower is calmer.
• Length of credit history — about 15%. The age of your oldest account, your newest, and the average of all of them.
• New credit — about 10%. How many accounts you’ve opened recently, and how many hard inquiries you’ve generated.
• Credit mix — about 10%. Whether you’ve handled more than one type of credit — revolving (cards) and installment (loans).

That’s it. There is no sixth secret category. There is no income line. The score does not know your salary, your job title, or your bank balance — only how you’ve handled borrowed money.

Why your number moves when “nothing changed”

The most common frustration is a score that drops five or ten points in a month you did nothing differently. Usually one of three things happened, and all three live inside the five inputs above:

1. A statement balance posted higher than usual. Utilization is measured the day the balance is reported, not the day you pay it. A normal month of spending can spike the reported number even if you pay in full days later.
2. An account aged off, or a new one lowered your average age. Opening a card helps your available credit but drops your average account age — two inputs pulling in opposite directions.
3. An inquiry landed. A single hard pull is small and temporary, but it’s real, and it shows up here.

None of this is mysterious once you know the categories. The “weather” was always a mechanism.

What this means for you

You don’t need a secret. You need to know which lever you’re pulling. Paying on time protects 35% of the score. Keeping reported balances low protects another 30%. Not opening accounts you don’t need protects the rest. Three habits, five inputs, one number.

We don’t repair credit and we don’t promise outcomes. We hand you the mechanics — what moves the number and why — so the decisions stay yours.

In the next pieces we’ll go deeper into utilization (the input people misread most often) and into the order of operations when your file is thin or brand new.