100 envelope challenge: tracker, random draw and finish date
Pick 100 or 50 envelopes, draw one at random, tick it when the money is in, and see when you will finish at your chosen pace.
Everything runs in your browser. Nothing you enter is sent anywhere.
How it works
Total = n × (n + 1) ÷ 2. For 100 envelopes that is 100 × 101 ÷ 2 = $5,050; for 50 it is 50 × 51 ÷ 2 = $1,275. The finish date is the envelopes you have left divided by your weekly pace, rounded up to whole weeks, counted from today.
An honest note about the size
The full 100-envelope version asks for $5,050. That is a big total for many budgets, and the random draw means a $90 envelope can come up in a tight week. If that sounds like too much, pick the 50-envelope version, or save toward a smaller goal in the savings goal calculator. The 50-envelope version still works the same way and totals $1,275. You can also leave the large envelopes until payday.
Making it work
Decide the weekly pace from your real surplus, not from the challenge. The budget planner shows what is left each month. If you would rather follow a fixed schedule, the 52-week challenge gives a dated table. Both are habits; where you put the money, and for what, is up to you.
Frequently asked questions
What is the 100-envelope challenge?
You number envelopes 1 to 100. Each time, you pick one at random and put in that many dollars. When all are filled you have saved 1 + 2 + … + 100 = $5,050.
Is $5,050 realistic?
For many households it is a large sum to find, and some of the later envelopes are big. If that is a stretch, use the 50-envelope version ($1,275 in total) or a smaller goal. A challenge you finish beats one you drop.
How does the random draw work?
The button picks one of the envelopes you have not yet ticked, with equal chance for each. It does not tick for you. Tick it once you have put the money in.
How is the finish date worked out?
Remaining envelopes ÷ envelopes per week, rounded up to whole weeks, counted from today. It is an estimate: it assumes you keep the pace and can find the money for whichever envelopes come up.
Are my ticks saved?
Yes, in this browser only. Nothing is sent anywhere. Switching the size between 50 and 100 keeps a separate record for each.