[noir_lord]

It can't speed up without an external force and at current slow rate it'll take about 2 trillion years to stop (this assumes a linear rate of slowing over time, which won't happen).

Much of the slowing is caused by tidal friction with the Moon (which recedes slightly each year), iirc eventually the Earth will become tidally locked with the Sun (same side facing all the time).

[saiya-jin]

we will lose moon well before that, it's going further away every year (don't recall exact value, should be few cm per year)