If something accumulates over a period of time, you can describe this with the adjective accrued. The principal in your bank account is so small, you'll never get rich off the accrued interest. You'd better plan on getting a job.
The adjective accrued comes from the Old French word acreu, meaning growth or increase, which is what the modern word describes as well — something that grows or accumulates over time. You forgot to pay your taxes on time. Now, with the accrued fees and penalties, you now owe twice as much as you did originally. The government is happy to take the extra money, but you should try to avoid that costly mistake in the future.