Project your monthly revenue for the next 12 to 36 months. Start from your current average month, add a growth rate, subtract churn on recurring revenue and shape the year with seasonality to get a month-by-month forecast, yearly totals and a chart.
Last updated:
Baseline & growth
$
Your typical (non-seasonal) month today.
%
New sales growth before churn.
%
Share of recurring revenue lost each month (cancellations, lost customers).
%
Churn applies only to this part. Use 0 for one-off sales.
Seasonality
%
Peak month is this much above average; the opposite month is this much below.
12 numbers. They are rescaled so the average is 100, so you can paste last year's monthly sales instead.
Enter your values to see the result.
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How to use the Sales Forecast Calculator
Enter your current average monthly revenue: a typical month without seasonal highs or lows.
Set the growth rate per month or per year, and the monthly churn for recurring revenue.
Choose seasonality: flat, one yearly peak, or 12 custom index values (or last year's monthly sales).
Pick the first month and forecast length (12 to 36 months).
Read the yearly totals and download the monthly forecast table as CSV.
The forecast formula
For each month m the calculator computes an underlying trend and then applies seasonality:
An annual growth rate is converted to a monthly one with (1 + annual)1/12 − 1. With the "one yearly peak" option the index follows a smooth curve: 100 + swing × cos(2π × months from peak ÷ 12), so the peak month is swing% above average and the opposite month the same amount below.
Example: $25,000 a month, 3% growth, 1.5% churn: net growth = 1.03 × 0.985 − 1 = 1.455% a month. Without seasonality month 12 is about $25,000 × 1.0145512 ≈ $29,732.
Net growth after churn (per month)
Gross growth
0% churn
1% churn
2% churn
5% churn
1%
1.00%
-0.01%
-1.02%
-4.05%
3%
3.00%
1.97%
0.94%
-2.15%
5%
5.00%
3.95%
2.90%
-0.25%
8%
8.00%
6.92%
5.84%
2.60%
10%
10.00%
8.90%
7.80%
4.50%
The table shows why reducing churn often matters as much as winning new sales: at 5% monthly churn even 5% gross growth leaves revenue slightly shrinking.
Tips for a better forecast
Build three scenarios (conservative, expected, optimistic) by changing only the growth rate, and plan spending on the conservative one.
Use real seasonality: paste two or three years of monthly sales averaged together for a steadier index.
Re-forecast monthly and compare with actual revenue to see whether your growth assumption holds.
Frequently asked questions
How do you forecast monthly sales?
A simple, transparent method is: forecast = baseline × (1 + net monthly growth)^month × seasonal index ÷ 100. Net growth combines new growth and churn: (1 + growth) × (1 − churn) − 1. This calculator applies that month by month and shows the working.
What is the difference between monthly and annual growth?
An annual rate compounds, so it is not divided by 12. 12% a year equals (1.12)^(1/12) − 1 = 0.949% a month, not 1%. Choose "per year" and the calculator converts it for you.
How does churn affect the forecast?
Churn removes a share of recurring revenue every month. With 3% growth and 1.5% churn, net growth is about 1.46% a month instead of 3%, which over 24 months is the difference between roughly 2.0× and 1.4× today's revenue.
What is a seasonal index?
A number for each month that shows how it compares with an average month (100). An index of 125 means the month usually sells 25% more than average; 80 means 20% less. Indexes are rescaled to average 100 so seasonality shifts revenue between months without changing the yearly trend.
Can I use last year's sales for seasonality?
Yes. Choose "Custom monthly index" and paste the 12 monthly sales figures from January to December. The calculator divides each by their average, so they become an index automatically.
How accurate is a sales forecast?
Any forecast is an estimate based on assumptions. Use it to plan cash, hiring and inventory, compare optimistic and conservative scenarios, and update it each month with actual results.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.