driftcurve

Overview

driftcurve is a free, open-source retirement modeling tool for households and people planning financial independence. It is best for users who want to model a household’s finances and compare assumptions, and are comfortable running a locally hosted app. Its breadth is a strength; basic tax modeling and setup requirements narrow its role.

Key features

Rather than treating retirement as a single portfolio, driftcurve supports multiple household members, account types, debts, mortgages, pensions, Social Security, and property sales. It also projects income, savings growth, and withdrawals. That makes it relevant when a plan depends on several people and types of assets or obligations; basic tax modeling is a meaningful limit for anyone who needs detailed tax planning. Account synchronization is not included, so users should expect to manage inputs themselves.

Default Monte Carlo simulations resample annual market data from 1966–2024, spanning equities, Treasuries, residential real estate, inflation, and Bitcoin. Users can recenter historical returns to their own long-run targets or set static annual assumptions. These options let a planner examine outcomes under different assumptions, but they do not make forecasts promises about future performance.

Risk-based spending guardrails solve for monthly spending and tie adjustments to portfolio thresholds and probability of success. This can help users explore withdrawal decisions with explicit conditions. The guardrails require a retirement year and a positive liquid portfolio, and a computation takes about 20–45 seconds, which can make repeated scenario adjustments less immediate.

A Compare page puts two scenarios on one chart, a useful way to inspect the effect of changing assumptions. In default local mode, household data and saved scenarios remain in browser localStorage, with no account or server-side database persistence; forecasts still run through the Python backend. Optional multi-user mode adds email/password accounts, server-side sessions, and profiles and scenarios stored in driftcurve.db. The documented API covers forecasts and guardrails, with authentication, profile, and scenario endpoints for multi-user mode. This flexibility favors technically comfortable users over people seeking a fully managed, account-based service.

Pricing

The Free plan costs nothing, with no subscription. It is self-hosted and has no accounts in default local mode. It includes income projection, savings growth projection, withdrawal planning, basic tax modeling, Social Security modeling, and scenario analysis. There is no free trial because the plan is free, and no seat or usage quota is stated. Its main trade-off is operational: setup involves creating a Python virtual environment, installing requirements, running the app with Uvicorn, and opening it at localhost:8000. The project is open source under the Apache License 2.0.

driftcurve is a modeling and educational tool, not a licensed financial, investment, tax, or legal advisor. Its outputs should not be treated as professional advice.

Platforms

driftcurve is available as a web app, API, and self-hosted software. The quick start runs the app locally at localhost:8000, so the self-hosted route suits users willing to handle a Python setup; it is less suited to anyone who expects a ready-to-use hosted service.

Who it's for

Choose driftcurve if you want to model several household members, debts, property, pensions, and retirement income together, and value control over return assumptions and scenario comparisons. It is particularly relevant to financial-independence planning. Look elsewhere if you need detailed tax modeling, account synchronization, or professional financial advice, or do not want to set up software locally.

Pros and cons

• Pro: Household inputs span people, assets, debts, and property, giving multi-part retirement scenarios more context than a portfolio-only view.
• Pro: Historical resampling, return recentering, and static assumptions provide distinct ways to examine market assumptions.
• Pro: Local storage keeps saved household data and scenarios in the browser in default mode, without account or server-side database persistence.
• Con: Basic tax modeling and no account synchronization leave users to handle important tax detail and keep inputs current.
• Con: Local Python setup and 20–45-second computations add friction, while guardrails also require a retirement year and positive liquid portfolio.

Alternatives

Boldin is worth considering if you prefer Android, iOS, or web access and want a free Basic plan with 100+ inputs, two interactive explorers, 10+ charts, and up to five Boldin AI questions per day; it also offers a free trial.

Flexible Retirement Planner is a free option for personal non-commercial use across Linux, macOS, web, and Windows, and may suit users who want broader desktop platform coverage.

ProjectionLab offers a free Basic plan with forecasting, financial planning, Monte Carlo simulations, historical backtesting, and flexible modeling, plus a free trial. Pick it if those named planning tools or Android and iOS access are a better fit.

RetireePlan is another free, open-source option, with API, self-hosted, web, and desktop platforms.

FI Calc is a free web calculator supported by donations; consider it for calculator access rather than driftcurve’s household modeling and self-hosted setup.

Fidelity Planning & Guidance Center is a free web plan generator, though investment expenses and account transaction fees may still apply.

FIRECalc provides a free core retirement calculator, with some additional features available on request through supporter registration.

Retireator is a free, open-source retirement simulator for web and Windows.

For a wider shortlist, see Retirement Planning Software. Database Schema Comparison Tools covers a separate software category.

Verdict

driftcurve is a strong fit for technically comfortable households and financial-independence planners who want a free, open-source way to model varied household finances and test retirement scenarios. Its main reasons to choose it are broad inputs, flexible return assumptions, and local data storage. Choose another tool if you need deeper tax support, synchronized accounts, or a simpler setup.