From Side Project to Startup: 15 Business Ideas You Can Start Tonight

In 2001, Ben Chestnut was running a web design agency. Clients kept asking him to set up email newsletters, and the process was painful every single time. So he built a simple tool to make it easier.

That tool was Mailchimp.

For seven years, Mailchimp was a side project. Chestnut kept running his agency. The email tool grew slowly, adding features when clients needed them, generating revenue without any venture capital.

By 2009, Mailchimp had grown enough that Chestnut shut down the agency and focused full-time on email. By 2021, Intuit acquired Mailchimp for $12 billion.

The story sounds unusual, but it's not. Some of the most successful companies in tech started exactly the same way.

GitHub started as a weekend project by Tom Preston-Werner while he worked at a startup called Powerset. He just wanted a better way to manage code. Microsoft bought GitHub for $7.5 billion.

Craigslist began as an email list Craig Newmark maintained for friends in San Francisco. He kept his day job for years. Today, Craigslist generates over $600 million in annual revenue with a team of about 50 people.

Instagram was a side project that Kevin Systrom built while working at a travel recommendations startup. He and his co-founder Mike Krieger launched it in 2010, and Facebook acquired it for $1 billion just 18 months later.

Twitter emerged from a side project at a podcasting company called Odeo. When Apple announced iTunes would handle podcasts, Odeo's core product became irrelevant. Jack Dorsey's side project became the company's new focus.

The pattern is consistent: founders with day jobs, solving real problems they encounter, building without pressure, and growing until the side project becomes too big to ignore.

The advantages of starting as a side project are significant. You have stable income while you experiment. You have time to find product-market fit without runway pressure. You can iterate based on customer feedback without panicking about burn rate. And if the idea doesn't work, you pivot without losing everything.

Here are 15 business ideas you can realistically start while keeping your day job.

SaaS and Software Ideas

1. Internal Tool as a Product

The idea: Take an internal tool your company built and productize it for others.

Slack started this way. Stewart Butterfield's team built an internal chat tool while developing their video game Glitch. When the game failed, the chat tool became a $27 billion company.

Target market: Other companies in your industry facing the same operational problem.

Revenue model: Monthly subscription. $29-299/month depending on team size and features.

How to validate tonight: List the internal tools your company has built. Which ones do other companies ask about? Which ones solve problems you've seen across multiple jobs? Post in relevant communities asking if others face the same problem.

Why it works as a side project: You've already built version 0.1 and validated the problem exists. The hard part is done.

2. Niche Vertical SaaS

The idea: Take generic software and specialize it for a specific industry.

Shopify is generic e-commerce. But there's room for e-commerce specialized for wine sellers, art galleries, or farm-to-table producers. Each niche has unique needs that generic tools handle poorly.

Target market: Pick an industry you know. Medical practices, law firms, construction companies, yoga studios, real estate agents. The more specific, the better.

Revenue model: Monthly subscription. $50-500/month. Niche industries often pay more because alternatives don't fit their needs.

How to validate tonight: Search "[industry] software frustrations" on Reddit and Twitter. What complaints keep appearing? Interview 5 people in the industry this week.

Why it works as a side project: Small markets don't attract big competitors. You can dominate a niche while keeping your day job, then expand later.

3. Browser Extension That Solves a Workflow Problem

The idea: Build a browser extension that automates something you do repeatedly.

Grammarly started as a browser extension. So did Honey (acquired by PayPal for $4 billion), Loom, and dozens of other successful products.

Target market: Anyone who does the same type of work you do.

Revenue model: Freemium with paid tier. $5-15/month for individuals, $10-30/user/month for teams.

How to validate tonight: What repetitive browser tasks do you do daily? What Chrome extensions do you use, and what do they do poorly? Check the Chrome Web Store reviews for competitors and note the complaints.

Why it works as a side project: Extensions are small, focused products. You can build an MVP in a weekend and iterate based on real usage.

4. API Integration Service

The idea: Connect two systems that don't talk to each other natively.

Zapier built a massive business connecting apps. But there's room for specialized integrations that Zapier handles poorly. Deep integrations between specific tools for specific workflows.

Target market: Users of both systems who need data to flow between them.

Revenue model: Monthly subscription or per-transaction pricing. $20-200/month depending on usage.

How to validate tonight: What manual data transfer do you do between systems at work? Search "[App A] [App B] integration" and see what people are asking for.

Why it works as a side project: Most integrations start small. You build for your own use case, then discover others have the same problem.

Services and Consulting Ideas

5. Fractional Expert Services

The idea: Offer your professional expertise on a part-time basis to companies that can't afford (or don't need) full-time hires.

Fractional CFOs, CTOs, CMOs, and other executives are in high demand. So are fractional specialists: data engineers, security experts, compliance officers.

Target market: Startups and small businesses that need expertise but not full-time headcount.

Revenue model: Monthly retainer ($2,000-10,000/month) or hourly ($150-400/hour).

How to validate tonight: Update your LinkedIn headline to "[Your expertise], available for fractional/advisory work." Post about what you can help with. Reach out to 10 startup founders in your network.

Why it works as a side project: You set the hours. Start with 5-10 hours/month for one client. Add more as you have capacity.

6. Implementation and Migration Services

The idea: Help companies implement, migrate to, or optimize specific software.

Salesforce has an entire ecosystem of implementation partners. So do HubSpot, Workday, and every major enterprise tool. But this works for smaller tools too.

Target market: Companies adopting new software who don't have internal expertise.

Revenue model: Project-based ($5,000-50,000) or ongoing retainer ($1,000-5,000/month).

How to validate tonight: What software are you an expert in? Search "[software name] implementation help" or "[software name] consultant" and see what exists. Check job boards for implementation roles at companies using that software.

Why it works as a side project: Projects are discrete. You can do one migration on weekends, then decide if you want more.

7. Done-For-You Agency Services

The idea: Take a task businesses struggle with and do it for them, systematically.

Content agencies, SEO agencies, paid ads agencies all work this way. But there's room for more specialized versions: podcast editing agencies, newsletter operations, customer research services.

Target market: Businesses that need the output but don't want to hire or learn the skill.

Revenue model: Monthly retainer ($500-5,000/month) or per-deliverable pricing.

How to validate tonight: What do you do well that others find difficult? What services do businesses in your network outsource? Post an offer to do one project for free in exchange for a testimonial.

Why it works as a side project: Start with one client. Systematize your process. Add clients as you refine your systems.

8. Coaching and Advisory for Career Transitions

The idea: Help people make the career transition you've already made.

Former investment bankers coach people trying to break into finance. Ex-FAANG employees help candidates prepare for tech interviews. People who've switched careers coach others through the same transition.

Target market: People 1-2 steps behind you on a path you've traveled.

Revenue model: Hourly coaching ($100-500/hour), packages ($500-5,000), or cohort programs ($500-2,000 per participant).

How to validate tonight: Write about your career journey on LinkedIn. Offer 3 free calls to people interested in making a similar transition. See what questions they ask and what problems they face.

Why it works as a side project: You schedule calls when you have time. The "product" is your experience, which requires no development.

Content and Education Ideas

9. Paid Newsletter in Your Area of Expertise

The idea: Write regularly about a topic you know deeply. Charge subscribers for access.

Lenny Rachitsky left Airbnb and started a newsletter about product management. It now generates over $1 million annually. Packy McCormick writes about business strategy. The Hustle sold to HubSpot for a reported $27 million.

Target market: Professionals who want to stay current or improve in your area of expertise.

Revenue model: Paid subscriptions ($10-30/month or $100-300/year). Or free newsletter with paid community/courses.

How to validate tonight: Start a free Substack. Write 5 posts about what you know. Share them in relevant communities. See who subscribes and what resonates.

Why it works as a side project: Writing takes a few hours per week. You can batch-write on weekends. The audience builds while you sleep.

10. Cohort-Based Course

The idea: Teach a live course to a group of students, running for 4-8 weeks.

Maven, the cohort-based course platform, has helped instructors generate millions in revenue. Courses on writing, product management, leadership, technical skills, and more.

Target market: Professionals who want structured learning with accountability and community.

Revenue model: Per-cohort pricing ($500-5,000 per student). Run 2-4 cohorts per year.

How to validate tonight: What do people ask you to teach them? What skill took you years to learn that you could compress into a curriculum? Pre-sell a cohort before building the course content.

Why it works as a side project: Cohorts are time-boxed. Run a 6-week course, then take a break. Scale by raising prices or increasing cohort size.

11. YouTube Channel or Podcast in a Professional Niche

The idea: Create video or audio content about your professional domain.

Professional niches work better than entertainment because viewers have commercial intent. They're trying to improve at their jobs. This means higher ad rates, easier sponsorship, and natural transitions to products.

Target market: Professionals in your field who learn through video or audio.

Revenue model: Ad revenue, sponsorships ($500-10,000/episode), affiliate income, and upsells to courses or services.

How to validate tonight: Search YouTube for your professional topic. Is it underserved? What questions aren't being answered well? Record your first video with your phone.

Why it works as a side project: Batch recording works well. Film 4 videos on a Saturday, release weekly. The content compounds over time.

E-commerce and Physical Product Ideas

12. Print-on-Demand for a Specific Community

The idea: Design products for a niche community and sell them without holding inventory.

Print-on-demand services (Printful, Printify, Gelato) handle production and shipping. You design products and market them.

Target market: Enthusiast communities with strong identity. Rock climbers, software developers, nurses, specific dog breeds, niche hobbies.

Revenue model: Product margin (typically 20-40% of sale price).

How to validate tonight: What communities are you part of? What inside jokes or shared experiences do members have? Design one product and post it to the community to gauge interest.

Why it works as a side project: No inventory risk. No shipping logistics. You can run ads and fulfill orders while you sleep.

13. Curated Subscription Box

The idea: Curate and ship a box of products to subscribers monthly.

Subscription boxes work for nearly every niche: coffee, snacks, books, craft supplies, pet products, beauty products.

Target market: Enthusiasts who want discovery and curation in a category they care about.

Revenue model: Monthly subscription ($20-100/box). Margin of 40-60% after product and shipping costs.

How to validate tonight: What category do you have taste in? What products do people ask you to recommend? Source products from local makers or wholesale suppliers and test with 10 prepaid subscribers.

Why it works as a side project: Batch your work. Source products one weekend. Pack boxes another weekend. Systemize and delegate as you grow.

14. Digital Products for Professionals

The idea: Create templates, tools, or resources that professionals use repeatedly.

Notion templates, Excel models, Figma UI kits, legal document templates, photography presets. Digital products that save professionals time.

Target market: Professionals who do repetitive work and value their time.

Revenue model: One-time purchase ($19-199) or subscription for ongoing updates.

How to validate tonight: What templates or tools have you built for yourself? What do coworkers ask you to share? List one product on Gumroad and share it in relevant communities.

Why it works as a side project: Create once, sell forever. No inventory, no shipping, no marginal cost per sale.

Marketplace and Platform Ideas

15. Niche Marketplace Connecting Supply and Demand

The idea: Build a marketplace for a specific category where buyers and sellers struggle to find each other.

Thumbtack for local services. Rover for pet sitting. Faire for wholesale retail. Every successful marketplace started in a niche before expanding.

Target market: A category where transactions happen but discovery is painful.

Revenue model: Transaction fee (5-20% of each sale) or subscription for sellers.

How to validate tonight: What transactions have you struggled to complete due to discovery problems? What do people in your network buy/sell that doesn't have a dedicated marketplace? Start by manually connecting buyers and sellers to validate demand before building any technology.

Why it works as a side project: Start with manual matchmaking. Be the marketplace before you build the marketplace. Only automate when volume justifies it.

How to Validate Before You Invest Time

The graveyard of side projects is filled with products nobody wanted. Validation prevents you from joining them.

Talk to potential customers first. Before writing any code or creating any product, have 20 conversations with people who might buy. Ask about their problems, not your solution. Listen for patterns.

Test demand with a landing page. Create a simple page describing your product and collect emails. If you can't get signups, you'll have trouble getting customers.

Try to get paid before building. The ultimate validation is prepayment. If someone will pay for something that doesn't exist yet, you've proven demand.

Set a validation timeline. Give yourself 2-4 weeks to validate. If you can't find evidence of demand in that window, move on.

Be honest about feedback. Polite enthusiasm from friends means nothing. Money is the only signal that counts. "I would buy this" is worthless. "Here's my credit card" is validation.

Time Management for Side Projects

The biggest challenge isn't ideas. It's finding time while holding a full-time job.

Protect specific hours. Block time on your calendar and defend it ruthlessly. Early mornings work for many people: 5-7am before the day starts. Others prefer evenings or dedicated weekend blocks.

Focus on one thing. Side projects fail when founders spread too thin. Choose one idea and commit to it for at least 3-6 months before evaluating.

Batch similar tasks. Write all your content in one session. Do all your customer calls on the same day. Context-switching kills productivity.

Ship small, iterate fast. Perfectionism is the enemy of side projects. Launch something minimal and improve based on feedback. Done is better than perfect.

Track progress, not hours. What matters is what you shipped, not how long you worked. Set weekly goals and hold yourself accountable.

When to Quit Your Job (And When Not To)

This is the question every side-project founder wrestles with.

Don't quit based on potential. "This could be huge" is not a reason to quit. Every founder thinks their idea could be huge. Wait for evidence.

Don't quit at the first sign of traction. One good month doesn't mean you've found product-market fit. Wait for consistent, repeatable growth.

Consider quitting when: Your side project generates 50-100% of your salary. You have 12-18 months of personal runway saved. Growth is accelerating and you're turning away customers because you don't have time. The opportunity cost of staying employed is clearly higher than the risk of leaving.

Never quit when: You're funded by optimism rather than revenue. You're running from your job rather than running toward your startup. Your family isn't aligned with the decision. You haven't validated that customers will pay.

The best founders quit later than they want to. They build proof before making the leap. They validate obsessively because they understand what's at stake.

Start Tonight, Learn Forever

The side project you start tonight probably won't become a billion-dollar company. But that's not the point.

Each side project teaches you something: how to ship, how to sell, how to listen to customers, how to iterate. These skills compound. The lessons from a failed side project make the next one more likely to succeed.

Mailchimp was Ben Chestnut's side project for seven years before it took off. He learned constantly. He iterated patiently. When the moment came, he was ready.

You don't need to quit your job to start a company. You need to start. Tonight.

Pick one idea from this list that matches your skills and interests. Validate it this week. Build something minimal this month. See what happens.

The worst case: you learn something valuable. The best case: you build the foundation for your next chapter.

Validate Your Side Project Idea

Not sure if your idea has legs? Bedrock Reports can help you understand the market before you invest serious time.

Our AI-powered validation reports analyze:

• Market size and growth potential
• Existing competitors and their weaknesses
• Customer segments most likely to pay
• Risks and challenges specific to your idea

Get evidence-backed research in minutes, not weeks. So you can focus your limited side-project time on ideas that actually have potential.

Keep Reading

• How to Validate a Business Idea - The complete validation playbook for any idea
• Founder-Market Fit Guide - Match ideas to your background and skills
• Trend Surfing for Startup Ideas - Find ideas positioned for future growth
• Pain Point Mining Tutorial - Discover problems worth solving from real customer frustrations

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Ready to validate your side project idea? Try Bedrock Reports free and get investor-grade research on any business concept.