Startup idea: Flexible Block Planner Instead of Time Blocking
Classic time-blocking doesn't fit people who naturally group tasks into flexible blocks ('work 4 hours, clean, portfolio') rather than planning by the hour.
Get the PRD prompt, $9.99 Market: $672K in 3 years
r/productivity · Sep 14, 2026 – Oct 14, 2026 · 29 upvotes
Does anyone else group tasks into flexible blocks…
Read the thread · 32 comments
Flexible Block Planner Instead of Time Blocking is a startup idea for knowledge workers and people with ADHD. Classic time-blocking doesn't fit people who naturally group tasks into flexible blocks ('work 4 hours, clean, portfolio') rather than planning by the hour. A thread in r/productivity drew 29 upvotes and 32 comments between Sep 14, 2026 – Oct 14, 2026. People get by with Sunsama, Akiflow, and Todoist, and that still leaves this job open. Hotness is 2.40, Cool. Mild annoyance. Price-sensitive audience. The thread drew 29 upvotes and 32 comments. Crowded with decent tools. Buildable in days. A first version is weekend-easy, about 2 weeks, priced under $10 a month and charged as a free tier and a paid upgrade. The pain, the source, the alternatives, the scope notes, and the questions on this page are free to read and free to build from. The agent starter prompt is the paid part. The first slice is on the page. One credit unlocks the rest, to paste into a coding agent, download as Markdown, or send as a private link.
Who has it
Knowledge workers and people with ADHD.
- Knowledge workers
- People with ADHD
- B2C
- Global
- r/productivity
What people use now
3 options, and the gap between them.
Sunsama
Akiflow
Todoist
Crowded with decent tools.
Flexible Block Planner Instead of Time Blocking is built for the part these leave undone.
A way through
A planner built around flexible, reorderable activity blocks without fixed start times: a middle format between a to-do list and a calendar.
MVP scope
The first version, in 2 weeks.
- 00 Goal
The one job
Plan your day as reorderable blocks of work with no fixed start times, halfway between a to-do list and a calendar.
- 01 Week 1
The core
Plan the day in flexible, reorderable activity blocks with no fixed start times.
- 02 Week 1
The follow-through
Sit between a to-do list and a calendar.
- 03 Week 2
How it ships
As a web app that opens in any browser, with nothing to install. No AI is needed for the first version.
- — Not in v1
Left out on purpose
Replacing Sunsama. Version one does the one job above and stops there.
How it could charge
The business model, at a glance.
- Model
- Freemium
- Price
- Under $10 a month
- Buyer
- PeopleAn individual or household pays
- Region
- Global
Hotness
Why it scores 2.40.
Mild annoyance. Price-sensitive audience. The thread drew 29 upvotes and 32 comments. Crowded with decent tools. Buildable in days.
29 upvotes 32 comments r/productivity Sep 14, 2026 – Oct 14, 2026 verified Oct 14, 2026 Thread ↗
Weights: pain 25%, willingness to pay 20%, demand 20%, gap 15%, ease 10%, recency 10%. Recency is recomputed every build. The source report’s 1–10 score is not shown.
Market size · estimate
How big this could get
A bottom-up estimate for Flexible Block Planner Instead of Time Blocking: real customer counts × a realistic price. Not a forecast.
$221M a year
4.6M adults · 30% of US adults with a current ADHD diagnosis
$67.2M a year
1.4M adults · app-store and community reach
$672K a year
14,000 adults · 1% of the reachable segment in three years
What that means
14,000 adults at $4/mo = $672K ARR
Medium confidenceHow we estimated this
- Base: 15,500,000 US adults with a current ADHD diagnosis.
- Has the problem: 30% (assume 30% have abandoned time blocking).
- Revenue per adult: $48 per year ($4/mo).
- Reachable: 30% (app-store and community reach).
- Three-year capture: 1% of the reachable segment.
TAM = customers with the problem × revenue per customer. SAM = the part an early product can reach. SOM = a conservative three-year share of SAM. Bars use a log scale. Shares marked “assume” are our judgment, not measured.
Take it to a build
Build Flexible Block Planner Instead of Time Blocking with an agent, or with us.
Agent starter prompt
$9.99 / 1 credit
A full PRD written for a coding agent: scope, data model, screens, edge cases, and the first week of tasks for this idea.
- Copy it straight into Claude Code, Cursor, or Codex.
- Download it as a .md file you keep.
- Send your bot a private link that refreshes every seven days.
# Agent starter prompt: Flexible Block Planner Instead of Time Blocking
You are a senior product engineer. Build only the product described in this document. If a detail is missing, choose the smallest option and write it down in the README. Do not invent a second product, a marketplace of marketplaces, or a growth hack.
## Product
Name: Flexible Block Planner Instead of Time Blocking
One line: Plan your day as reorderable blocks of work with no fixed start times, halfway between a to-do list and a calendar.
Shape: Web app
AI stance: No AI needed
Region for v1: Global
Hotness (context only, not a requirement): 2.40 (cool). Mild annoyance; price-sensitive audience; thread engagement 29▲/32💬 (demand 1/5); crowded with decent tools; buildable in days.
## Problem
Classic time-blocking doesn't fit people who naturally group tasks into flexible blocks ('work 4 hours, clean, portfolio') rather than planning by the hour.
Who feels it: Knowledge workers and people with ADHD.
The first slice is above. The rest unlocks for 1 credit and is never in this page’s HTML.
Credits work on both sites. On Business Ideas to Build the same credit unlocks the business plan and growth playbook for Flexible Block Planner Instead of Time Blocking.
Or we build it
Your first version, shipped by our team.
A working product in your repo, built from this PRD. You own the code.
$1,000 scoping fee, credited toward the build.
Equity instead of cash is an application, not a checkout →Questions
Is this idea already taken?
People already use Sunsama, Akiflow, Todoist. Those options do not do the job in the solution above. The idea is free to build. Nothing here is an exclusive claim.
How hard is a first version?
Weekend-easy. A tight MVP is about 2 weeks (2 weeks), assuming the regulated or partner-gated parts are stubbed. The paid prompt turns that into tasks.
Who would pay, and how?
The audience is knowledge workers and people with ADHD. Charge a free tier and a paid upgrade, and test a price under $10 a month. Willingness to pay is one input to Hotness, not a promise that someone will buy.
Can I use the evidence?
Yes. Build the product. The thread title is a short excerpt with a link, not a quote we are putting in someone's mouth. Exact post dates and verbatim lines are added only after a manual check. Ideas are suggestions, not medical, legal, or financial advice.
The sister site keeps a business plan and a growth playbook for the same pain. Draft the business plan