You can learn about all of the assumptions that go into Betterment's retirement planning methodology here.
Many of the assumptions that we make can be modified by selecting your primary retirement goal from the menu and then "Plan". Once you click "Edit Assumptions" you'll be able to edit and review the following:
- Social Security assumptions
- Age you plan to retire
- Assumed lifespan
- Inflation rate
- Rate of return for synced external accounts
- Annual savings assumptions
For more accurate retirement planning advice, you can securely sync external accounts you're using for retirement.