If 10 year bonds double from 2 to 4% it will take 10 years for...

If 10 year bonds double from 2 to 4% it will take 10 years for the interest paid to double. All the bonds sold in the last 10 years don't change in the interest they earn from the US govt.

If you are an investor and are holding a $100 10 year bond at say 2% interest with 9 years to maturity and rates go up to 4% then if you want to sell your $100 bond you will only get say $85 which is the difference in the next 9 years at 2% versus 4% interest.

In looking at ten year bonds from the US Govt. point of view if 10 year bonds increase from 2% to 4% then after 1 year the average interest they will be paying over all their 10 year bonds is 2.2% (9 years worth of bonds at 2% & 1 year worth at 4%) after 2 years the average is 2.4%. Only after 10 years will their interest be at 4%.

The US Govt even after 1 year at 4% is hardly paying any extra interest. In reality bonds already sold to investors are a mix of all sorts of time frames from months to 30 years and all at various interest rates which were appropriate at the time. Even if rates rise quickly there is a huge backlog of bonds already fixed at low rates which have to be churned through before extra interest has to be paid. So a spike in interest rates will take years flow through fully so its totally wrong to be suggesting the US Govt. is paying 50% more interest right now.