About this calculator
Will your subscription business keep growing, or does churn eventually cancel out your new sign-ups? This calculator simulates it. Enter where you start, how many customers you add each month, what they pay and how many leave, and it shows your revenue at the end of the period.
The most useful figure is the level your customer base levels off at, which is where the customers you lose each month equal the ones you gain.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
100 customers, 20 new a month, 5% churn, £30 a month
- Monthly revenue in month 12
- £7,136.76
- Total revenue over 12 months
- £65,401.57
- Annual run rate at the end
- £85,641.12
- Customers at the end
- 238
- Customers you'd level off at
- 400
- Average customer lifetime
- 20 months
Starting with 100 customers, adding 20 a month and losing 5% a month, you'd have about 238 customers after 12 months, earning £7,136.76 a month.
Starting from nothing: 30 new a month, 8% churn, £15, 24 months
- Monthly revenue in month 24
- £4,864.62
- Total revenue over 24 months
- £79,056.86
- Annual run rate at the end
- £58,375.44
- Customers at the end
- 324
- Customers you'd level off at
- 375
- Average customer lifetime
- 12.5 months
Starting with 0 customers, adding 30 a month and losing 8% a month, you'd have about 324 customers after 24 months, earning £4,864.62 a month.
No new sign-ups: 500 customers, 4% churn, £20
- Monthly revenue in month 12
- £6,127.10
- Total revenue over 12 months
- £92,949.66
- Annual run rate at the end
- £73,525.20
- Customers at the end
- 306
- Customers you'd level off at
- 0
- Average customer lifetime
- 25 months
Starting with 500 customers, adding 0 a month and losing 4% a month, you'd have about 306 customers after 12 months, earning £6,127.10 a month.
How the forecast works
Each month, the churn percentage is taken off the customers you had at the start of that month, and then the new customers join:
customers next month = customers this month × (1 − churn) + new customers
Revenue for the month is the customers at the end of it multiplied by the price. The total adds every month together.
Why growth levels off
With steady sign-ups and steady churn, you can't grow forever. Your base settles where the customers you lose equal the customers you gain: new customers per month ÷ monthly churn. Adding 20 customers a month with 5% churn levels off at 400 customers. To grow beyond that you have to add more customers or lose fewer.
That's why cutting churn is often worth more than finding new customers: it raises the ceiling as well as slowing the leak.
Limits of any forecast
This assumes new customers, price and churn stay constant, which real businesses rarely do. Churn is often highest in the first months after sign-up, and prices, sign-ups and seasons change. Use it to compare scenarios, for example what happens if churn falls from 5% to 4%, rather than to predict your exact income.
Frequently asked questions
How do I forecast subscription revenue?
Start with your current customers, remove the monthly churn, add the new sign-ups, and multiply by the price. Repeat for each month. This calculator does it for you.
What is a good churn rate?
It varies a lot between products and customer types, and monthly churn for consumer products is usually higher than for business products. Compare with your own history and aim to bring it down over time.
What does “levels off” mean?
It's the size your customer base settles at when the customers you lose each month equal the customers you gain. It's new customers per month divided by monthly churn.
Does this include annual plans?
Convert annual plans to a monthly amount (divide by 12) and use the average price per customer. It doesn't model a customer's renewal date.
Can I model growing sign-ups?
Not in this version, which uses a steady number of new customers each month. Run several scenarios with different numbers to compare.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.