Um...your math seems a bit off.

We've had Federal Debt since 1789. Woodrow Wilson took he previous $2.9 billion and made it into $23.9 billion by 1921. Harding/Coolidge removed $7 billion of that debt by the end of 1929. And every President afterwards increased that debt overall for their term. Ike and Truman had a few years of surpluses.

FDR added a whopping $236 billion in debt. So, we can start there at 1945.
In 72 years, we added $20 trillion in debt.
$10 trillion of that was in the last 8 years.

At last years $1.4 trillion deficit, we would hit $40 trillion in just over 7 years.
However, we are only at $690 billion this year.

Also, the government year ends at the end of September, which is why the spending isn't constant over the year.